Optimize working with filters and extensions in FileDialog, decrease allocations (#9599)

* remove unnecessary split allocation, return extensions as ROS<string>

* remove CAS remarks, finish up with the rest

* use MemoryExtensions.Count instead of SpanSplitEnumerator<char> (edwardneal)

* simplify Slice, use ContainsAny instead of IndexAny (halgab)

* Post-merge issues

Author: h3xds1nz

src/Microsoft.DotNet.Wpf/src/PresentationFramework/MS/Internal/AppModel/ShellProvider.cs

@@ -24,12 +24,18 @@ namespace MS.Internal.AppModel
     #region Structs
 
     [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
-    internal struct COMDLG_FILTERSPEC
+    internal readonly struct COMDLG_FILTERSPEC
     {
         [MarshalAs(UnmanagedType.LPWStr)]
-        public string pszName;
+        public readonly string pszName;
         [MarshalAs(UnmanagedType.LPWStr)]
-        public string pszSpec;
+        public readonly string pszSpec;
+
+        public COMDLG_FILTERSPEC(string name, string spec)
+        {
+            pszName = name;
+            pszSpec = spec;
+        }
     }
 
     [StructLayout(LayoutKind.Sequential, Pack = 4)]

src/Microsoft.DotNet.Wpf/src/PresentationFramework/Microsoft/Win32/CommonDialog.cs

@@ -28,19 +28,8 @@ namespace Microsoft.Win32
     /// <summary>
     ///  An abstract base class for displaying common dialogs.
     /// </summary>
-    /// <Remarks>
-    ///     InheritanceDemand for UIPermission (UIPermissionWindow.AllWindows)
-    /// </Remarks>
     public abstract class CommonDialog
     {
-        //---------------------------------------------------
-        //
-        // Constructors
-        //
-        //---------------------------------------------------
-        //#region Constructors
-        //#endregion Constructors
-
         //---------------------------------------------------
         //
         // Public Methods
@@ -60,10 +49,7 @@ public abstract class CommonDialog
         ///  performs initialization tasks for all common dialogs and then
         ///  calls RunDialog.
         /// </summary>
-        /// <Remarks>
-        ///     Callers must have UIPermission(UIPermissionWindow.AllWindows) to call this API.
-        /// </Remarks>
-        public virtual Nullable<bool> ShowDialog()
+        public virtual bool? ShowDialog()
         {
             CheckPermissionsToShowDialog();
 
@@ -126,10 +112,7 @@ public virtual Nullable<bool> ShowDialog()
         /// <summary>
         ///  Runs a common dialog box, with the owner as the given Window
         /// </summary>
-        /// <Remarks>
-        ///     Callers must have UIPermission(UIPermissionWindow.AllWindows) to call this API.
-        /// </Remarks>
-        public Nullable<bool> ShowDialog(Window owner)
+        public bool? ShowDialog(Window owner)
         {
             CheckPermissionsToShowDialog();
 
@@ -200,14 +183,6 @@ public object Tag
 
         #endregion Public Properties
 
-        //---------------------------------------------------
-        //
-        // Public Events
-        //
-        //---------------------------------------------------
-        //#region Public Events
-        //#endregion Public Events
-
         //---------------------------------------------------
         //
         // Protected Methods
@@ -331,38 +306,6 @@ private void MoveToScreenCenter(HandleRef hWnd)
 
         #endregion Internal Methods
 
-        //---------------------------------------------------
-        //
-        // Internal Properties
-        //
-        //---------------------------------------------------
-        //#region Internal Properties
-        //#endregion Internal Properties
-
-        //---------------------------------------------------
-        //
-        // Internal Events
-        //
-        //---------------------------------------------------
-        //#region Internal Events
-        //#endregion Internal Events
-
-        //---------------------------------------------------
-        //
-        // Private Methods
-        //
-        //---------------------------------------------------
-        //#region Private Methods
-        //#endregion Private Methods
-
-        //---------------------------------------------------
-        //
-        // Protected Properties
-        //
-        //---------------------------------------------------
-        //#region Protected Properties
-        //#endregion Protected Properties
-
         //---------------------------------------------------
         //
         // Private Fields
@@ -373,7 +316,7 @@ private void MoveToScreenCenter(HandleRef hWnd)
         // Private variable used to store data for the Tag property
         private object _userData;
 
-        private Thread _thread = Thread.CurrentThread;
+        private readonly Thread _thread = Thread.CurrentThread;
 
         /// <summary>
         ///  The owner hwnd passed into the dialog is stored as a private

src/Microsoft.DotNet.Wpf/src/PresentationFramework/Microsoft/Win32/CommonItemDialog.cs

@@ -500,14 +500,6 @@ private protected string[] CloneItemNames()
 
         #endregion Internal Properties
 
-        //---------------------------------------------------
-        //
-        // Internal Events
-        //
-        //---------------------------------------------------
-        //#region Internal Events
-        //#endregion Internal Events
-
         //---------------------------------------------------
         //
         // Private Methods
@@ -697,10 +689,10 @@ private protected sealed class VistaDialogEvents : IFileDialogEvents, IDisposabl
         {
             public delegate bool OnOkCallback(IFileDialog dialog);
 
-            private IFileDialog _dialog;
+            private readonly IFileDialog _dialog;
 
-            private OnOkCallback _okCallback;
-            uint _eventCookie;
+            private readonly OnOkCallback _okCallback;
+            private readonly uint _eventCookie;
 
             public VistaDialogEvents(IFileDialog dialog, OnOkCallback okCallback)
             {