refactor: Adjust DataGrid Debug.Assert for Uno Platform compatibility (#3653)

## PR Type
What kind of change does this PR introduce?
- Refactoring (no functional changes, no api changes)

## What is the new behavior?

This changes aliases `System.Diagnostics.Debug` so that it does not conflict with Android's `View.Debug` property when building the DataGrid control for Xamarin.Android using the Uno Platform.

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tested code with current [supported SDKs](../readme.md#supported)
- [ ] Pull Request has been submitted to the documentation repository [instructions](..\contributing.md#docs). Link: <!-- docs PR link -->
- [ ] Sample in sample app has been added / updated (for bug fixes / features)
    - [ ] Icon has been created (if new sample) following the [Thumbnail Style Guide and templates](https://github.com/windows-toolkit/WindowsCommunityToolkit-design-assets)
- [ ] New major technical changes in the toolkit have or will be added to the [Wiki](https://github.com/windows-toolkit/WindowsCommunityToolkit/wiki) e.g. build changes, source generators, testing infrastructure, sample creation changes, etc...
- [ ] Tests for the changes have been added (for bug fixes / features) (if applicable)
- [ ] Header has been added to all new source files (run *build/UpdateHeaders.bat*)
- [x] Contains **NO** breaking changes

<!-- If this PR contains a breaking change, please describe the impact and migration path for existing applications below. 
     Please note that breaking changes are likely to be rejected within minor release cycles or held until major versions. -->


## Other information

Author: msftbot[bot]

Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/CollectionViews/ListCollectionView.cs

@@ -12,6 +12,8 @@
 using System.Reflection; // ConstructorInfo
 #endif
 
+using DiagnosticsDebug = System.Diagnostics.Debug;
+
 namespace Microsoft.Toolkit.Uwp.UI.Data.Utilities
 {
     /// <summary>
@@ -563,7 +565,7 @@ public object AddNew()
                 BeginAddNew(newItem, index);
             }
 
-            Debug.Assert(_newItemIndex != -2 && object.Equals(newItem, _newItem), "AddNew did not raise expected events");
+            DiagnosticsDebug.Assert(_newItemIndex != -2 && object.Equals(newItem, _newItem), "AddNew did not raise expected events");
 
             MoveCurrentTo(newItem);
 
@@ -588,7 +590,7 @@ public object AddNew()
         // related to AddNew.  This method is called from ProcessCollectionChanged.
         private void BeginAddNew(object newItem, int index)
         {
-            Debug.Assert(_newItemIndex == -2 && _newItem == NoNewItem, "unexpected call to BeginAddNew");
+            DiagnosticsDebug.Assert(_newItemIndex == -2 && _newItem == NoNewItem, "unexpected call to BeginAddNew");
 
             // remember the new item and its position in the underlying list
             SetNewItem(newItem);
@@ -810,7 +812,7 @@ private void SetNewItem(object item)
         {
             if (!object.Equals(item, _newItem))
             {
-                Debug.Assert(item == NoNewItem || this._newItem == NoNewItem, "Old and new _newItem values are unexpectedly different from NoNewItem");
+                DiagnosticsDebug.Assert(item == NoNewItem || this._newItem == NoNewItem, "Old and new _newItem values are unexpectedly different from NoNewItem");
                 _newItem = item;
 
                 OnPropertyChanged(CurrentAddItemPropertyName);
@@ -1193,7 +1195,7 @@ private void SetEditItem(object item)
         {
             if (!object.Equals(item, _editItem))
             {
-                Debug.Assert(item == null || _editItem == null, "Old and new _editItem values are unexpectedly non null");
+                DiagnosticsDebug.Assert(item == null || _editItem == null, "Old and new _editItem values are unexpectedly non null");
                 _editItem = item;
 
                 OnPropertyChanged(CurrentEditItemPropertyName);
@@ -1543,7 +1545,7 @@ private void ProcessCollectionChangedWithAdjustedIndex(EffectiveNotifyCollection
                     break;
 
                 default:
-                    Debug.Assert(false, "Unexpected Effective Collection Change Action");
+                    DiagnosticsDebug.Assert(false, "Unexpected Effective Collection Change Action");
                     break;
             }
 
@@ -1571,7 +1573,7 @@ private void ProcessCollectionChangedWithAdjustedIndex(EffectiveNotifyCollection
                 // so any changes to the current item will only be raised once, and from this method
                 // _currentChangedMonitor is used to guard whether the CurrentChanged and CurrentChanging event can be fired
                 // so by entering it we're preventing the base calls from firing those events.
-                Debug.Assert(!CurrentChangedMonitor.Busy, "Expected _currentChangedMonitor.Busy is false.");
+                DiagnosticsDebug.Assert(!CurrentChangedMonitor.Busy, "Expected _currentChangedMonitor.Busy is false.");
 
                 CurrentChangedMonitor.Enter();
                 using (CurrentChangedMonitor)
@@ -1910,23 +1912,23 @@ private void Debug_ValidateCollectionChangedEventArgs(NotifyCollectionChangedEve
             switch (e.Action)
             {
                 case NotifyCollectionChangedAction.Add:
-                    Debug.Assert(e.NewItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.NewItems.Count for Add action");
+                    DiagnosticsDebug.Assert(e.NewItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.NewItems.Count for Add action");
                     break;
 
                 case NotifyCollectionChangedAction.Remove:
-                    Debug.Assert(e.OldItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.OldItems.Count for Remove action");
+                    DiagnosticsDebug.Assert(e.OldItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.OldItems.Count for Remove action");
                     break;
 
                 case NotifyCollectionChangedAction.Replace:
-                    Debug.Assert(e.OldItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.OldItems.Count for Replace action");
-                    Debug.Assert(e.NewItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.NewItems.Count for Replace action");
+                    DiagnosticsDebug.Assert(e.OldItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.OldItems.Count for Replace action");
+                    DiagnosticsDebug.Assert(e.NewItems.Count == 1, "Unexpected NotifyCollectionChangedEventArgs.NewItems.Count for Replace action");
                     break;
 
                 case NotifyCollectionChangedAction.Reset:
                     break;
 
                 default:
-                    Debug.Assert(false, "Unexpected NotifyCollectionChangedEventArgs action");
+                    DiagnosticsDebug.Assert(false, "Unexpected NotifyCollectionChangedEventArgs action");
                     break;
             }
         }
@@ -2308,7 +2310,7 @@ private void SetSortDescriptions(SortDescriptionCollection descriptions)
 
             if (_sort != null)
             {
-                Debug.Assert(_sort.Count == 0, "must be empty SortDescription collection");
+                DiagnosticsDebug.Assert(_sort.Count == 0, "must be empty SortDescription collection");
                 ((INotifyCollectionChanged)_sort).CollectionChanged += new NotifyCollectionChangedEventHandler(SortDescriptionsChanged);
             }
         }

Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/DataGrid/Automation/DataGridAutomationPeer.cs

@@ -15,6 +15,8 @@
 using Windows.UI.Xaml.Controls.Primitives;
 using Windows.UI.Xaml.Data;
 
+using DiagnosticsDebug = System.Diagnostics.Debug;
+
 namespace Microsoft.Toolkit.Uwp.UI.Automation.Peers
 {
     /// <summary>
@@ -286,8 +288,8 @@ IRawElementProviderSimple IGridProvider.GetItem(int row, int column)
                     column++;
                 }
 
-                Debug.Assert(column >= 0, "Expected positive column value.");
-                Debug.Assert(column < this.OwningDataGrid.ColumnsItemsInternal.Count, "Expected smaller column value.");
+                DiagnosticsDebug.Assert(column >= 0, "Expected positive column value.");
+                DiagnosticsDebug.Assert(column < this.OwningDataGrid.ColumnsItemsInternal.Count, "Expected smaller column value.");
                 DataGridCell cell = dgr.Cells[column];
                 AutomationPeer peer = CreatePeerForElement(cell);
                 if (peer != null)
@@ -557,8 +559,8 @@ private AutomationPeer GetCellPeer(int slot, int column)
                 DataGridRow row = this.OwningDataGrid.DisplayData.GetDisplayedElement(slot) as DataGridRow;
                 if (row != null)
                 {
-                    Debug.Assert(column >= 0, "Expected positive column value.");
-                    Debug.Assert(column < this.OwningDataGrid.ColumnsItemsInternal.Count, "Expected smaller column value.");
+                    DiagnosticsDebug.Assert(column >= 0, "Expected positive column value.");
+                    DiagnosticsDebug.Assert(column < this.OwningDataGrid.ColumnsItemsInternal.Count, "Expected smaller column value.");
                     DataGridCell cell = row.Cells[column];
                     return CreatePeerForElement(cell);
                 }

Microsoft.Toolkit.Uwp.UI.Controls.DataGrid/DataGrid/Automation/DataGridGroupItemAutomationPeer.cs

@@ -14,6 +14,8 @@
 using Windows.UI.Xaml.Automation.Provider;
 using Windows.UI.Xaml.Data;
 
+using DiagnosticsDebug = System.Diagnostics.Debug;
+
 namespace Microsoft.Toolkit.Uwp.UI.Automation.Peers
 {
     /// <summary>
@@ -467,8 +469,8 @@ IRawElementProviderSimple IGridProvider.GetItem(int row, int column)
                 {
                     // Adjust the row index to be relative to the DataGrid instead of the group
                     row = groupInfo.Slot - this.OwningDataGrid.RowGroupHeadersTable.GetIndexCount(0, groupInfo.Slot) + row + 1;
-                    Debug.Assert(row >= 0, "Expected positive row.");
-                    Debug.Assert(row < this.OwningDataGrid.DataConnection.Count, "Expected row smaller than this.OwningDataGrid.DataConnection.Count.");
+                    DiagnosticsDebug.Assert(row >= 0, "Expected positive row.");
+                    DiagnosticsDebug.Assert(row < this.OwningDataGrid.DataConnection.Count, "Expected row smaller than this.OwningDataGrid.DataConnection.Count.");
                     int slot = this.OwningDataGrid.SlotFromRowIndex(row);
 
                     if (!this.OwningDataGrid.IsSlotVisible(slot))
@@ -477,12 +479,12 @@ IRawElementProviderSimple IGridProvider.GetItem(int row, int column)
                         this.OwningDataGrid.ScrollIntoView(item, this.OwningDataGrid.Columns[column]);
                     }
 
-                    Debug.Assert(this.OwningDataGrid.IsSlotVisible(slot), "Expected OwningDataGrid.IsSlotVisible(slot) is true.");
+                    DiagnosticsDebug.Assert(this.OwningDataGrid.IsSlotVisible(slot), "Expected OwningDataGrid.IsSlotVisible(slot) is true.");
 
                     DataGridRow dgr = this.OwningDataGrid.DisplayData.GetDisplayedElement(slot) as DataGridRow;
 
                     // the first cell is always the indentation filler cell if grouping is enabled, so skip it
-                    Debug.Assert(column + 1 < dgr.Cells.Count, "Expected column + 1 smaller than dgr.Cells.Count.");
+                    DiagnosticsDebug.Assert(column + 1 < dgr.Cells.Count, "Expected column + 1 smaller than dgr.Cells.Count.");
                     DataGridCell cell = dgr.Cells[column + 1];
                     AutomationPeer peer = CreatePeerForElement(cell);
                     if (peer != null)