Add ActivatableListView with cell activation support

- Introduced a new class for enhanced list view functionality
- Added support for activating cells with custom actions
- Implemented disposal management for activated cells
- Created an extension method for easier usage of cell activation

Author: michaelstonis

Stellar.Maui/ActivatableListView.cs

@@ -0,0 +1,61 @@
+using System.Collections.Concurrent;
+
+namespace Stellar.Maui;
+
+public class ActivatableListView : ListView
+{
+    private readonly ConcurrentDictionary<Cell, IDisposable> _cellActivators = new();
+
+    private Action<CompositeDisposable, Cell, int> _cellActivatedAction;
+
+    public IDisposable SetCellActivationAction(Action<CompositeDisposable, Cell, int> cellActivatedAction)
+    {
+        _cellActivatedAction = cellActivatedAction;
+
+        return Disposable.Create(
+            this,
+            x =>
+            {
+                x._cellActivatedAction = null;
+
+                foreach (var cellItem in x._cellActivators)
+                {
+                    cellItem.Value?.Dispose();
+                }
+
+                x._cellActivators.Clear();
+            });
+    }
+
+    protected override void SetupContent(Cell content, int index)
+    {
+        base.SetupContent(content, index);
+
+        if (_cellActivatedAction == null || _cellActivators.ContainsKey(content))
+        {
+            return;
+        }
+
+        var disposable = new CompositeDisposable();
+        _cellActivatedAction(disposable, content, index);
+        _cellActivators.AddOrUpdate(content, disposable, (k, v) => disposable);
+    }
+
+    protected override void UnhookContent(Cell content)
+    {
+        if (_cellActivators.TryRemove(content, out var disposable))
+        {
+            disposable?.Dispose();
+        }
+
+        base.UnhookContent(content);
+    }
+}
+
+public static class ActivatableListViewExtensions
+{
+    public static IDisposable WhenCellActivated(this ActivatableListView reactiveList, Action<CompositeDisposable, Cell, int> whenCellActivated)
+    {
+        return reactiveList.SetCellActivationAction(whenCellActivated);
+    }
+}