Make top level Handle* methods internal.

src/Avalonia.Controls/TopLevel.cs

@@ -529,7 +529,7 @@ namespace Avalonia.Controls
         /// Handles a paint notification from <see cref="ITopLevelImpl.Resized"/>.
         /// </summary>
         /// <param name="rect">The dirty area.</param>
-        protected virtual void HandlePaint(Rect rect)
+        private void HandlePaint(Rect rect)
         {
             Renderer.Paint(rect);
         }
@@ -537,7 +537,7 @@ namespace Avalonia.Controls
         /// <summary>
         /// Handles a closed notification from <see cref="ITopLevelImpl.Closed"/>.
         /// </summary>
-        protected virtual void HandleClosed()
+        private protected virtual void HandleClosed()
         {
             Renderer.SceneInvalidated -= SceneInvalidated;
             // We need to wait for the renderer to complete any in-flight operations
@@ -595,7 +595,7 @@ namespace Avalonia.Controls
         /// <see cref="ITopLevelImpl.ScalingChanged"/>.
         /// </summary>
         /// <param name="scaling">The window scaling.</param>
-        protected virtual void HandleScalingChanged(double scaling)
+        private void HandleScalingChanged(double scaling)
         {
             LayoutHelper.InvalidateSelfAndChildrenMeasure(this);
             ScalingChanged?.Invoke(this, EventArgs.Empty);
@@ -615,7 +615,7 @@ namespace Avalonia.Controls
             return false;
         }
 
-        protected virtual void HandleTransparencyLevelChanged(WindowTransparencyLevel transparencyLevel)
+        private void HandleTransparencyLevelChanged(WindowTransparencyLevel transparencyLevel)
         {
             if(_transparencyFallbackBorder != null)
             {

src/Avalonia.Controls/Window.cs

@@ -535,7 +535,7 @@ namespace Avalonia.Controls
             return true;
         }
 
-        protected virtual void HandleWindowStateChanged(WindowState state)
+        private void HandleWindowStateChanged(WindowState state)
         {
             WindowState = state;
 
@@ -979,7 +979,7 @@ namespace Avalonia.Controls
             return ClientSize;
         }
 
-        protected sealed override void HandleClosed()
+        private protected sealed override void HandleClosed()
         {
             RaiseEvent(new RoutedEventArgs(WindowClosedEvent));
 

src/Avalonia.Controls/WindowBase.cs

@@ -226,7 +226,7 @@ namespace Avalonia.Controls
         /// <param name="e">An <see cref="EventArgs"/> that contains the event data.</param>
         protected virtual void OnResized(WindowResizedEventArgs e) => Resized?.Invoke(this, e);
 
-        protected override void HandleClosed()
+        private protected override void HandleClosed()
         {
             using (FreezeVisibilityChangeHandling())
             {