TopLevel: avoid capturing of this reference when listening for property changes of PointerOverElement (#12996)

Co-authored-by: Dmitry Zhelnin <d.zhelnin@of-group.ru>

src/Avalonia.Controls/TopLevel.cs

@@ -153,6 +153,20 @@ namespace Avalonia.Controls
                     }
                 }
             });
+
+            PointerOverElementProperty.Changed.AddClassHandler<TopLevel>((topLevel, e) =>
+            {
+                if (e.OldValue is InputElement oldInputElement)
+                {
+                    oldInputElement.PropertyChanged -= topLevel.PointerOverElementOnPropertyChanged;
+                }
+
+                if (e.NewValue is InputElement newInputElement)
+                {
+                    topLevel.PlatformImpl?.SetCursor(newInputElement.Cursor?.PlatformImpl);
+                    newInputElement.PropertyChanged += topLevel.PointerOverElementOnPropertyChanged;
+                }
+            });
         }
 
         /// <summary>
@@ -215,11 +229,6 @@ namespace Avalonia.Controls
             ClientSize = impl.ClientSize;
             FrameSize = impl.FrameSize;
 
-            this.GetObservable(PointerOverElementProperty)
-                .Select(
-                    x => (x as InputElement)?.GetObservable(CursorProperty) ?? Observable.Empty<Cursor>())
-                .Switch().Subscribe(cursor => PlatformImpl?.SetCursor(cursor?.PlatformImpl));
-
             if (((IStyleHost)this).StylingParent is IResourceHost applicationResources)
             {
                 _resourcesChangesSubscriber = new TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>(
@@ -751,6 +760,14 @@ namespace Avalonia.Controls
             }
         }
 
+        private void PointerOverElementOnPropertyChanged(object? sender, AvaloniaPropertyChangedEventArgs e)
+        {
+            if (e.Property == CursorProperty && sender is InputElement inputElement)
+            {
+                PlatformImpl?.SetCursor(inputElement.Cursor?.PlatformImpl);
+            }
+        }
+
         private void GlobalActualThemeVariantChanged(object? sender, EventArgs e)
         {
             SetValue(ActualThemeVariantProperty, ((IThemeVariantHost)sender!).ActualThemeVariant, BindingPriority.Template);