Fix dev tools adorner highlight (#14883)

src/Avalonia.Diagnostics/Diagnostics/Views/TreePageView.xaml

@@ -8,7 +8,8 @@
               BorderThickness="0"
               ItemsSource="{Binding Nodes}"
               SelectedItem="{Binding SelectedNode, Mode=TwoWay}"
-              PointerMoved="UpdateAdorner">
+              PointerMoved="UpdateAdorner"
+              PointerExited="RemoveAdorner">
       <TreeView.DataTemplates>
         <TreeDataTemplate DataType="vm:TreeNode"
                           ItemsSource="{Binding Children}">

src/Avalonia.Diagnostics/Diagnostics/Views/TreePageView.xaml.cs

@@ -51,6 +51,12 @@ namespace Avalonia.Diagnostics.Views
             _adorner = Controls.ControlHighlightAdorner.Add(visual, visualizeMarginPadding: shouldVisualizeMarginPadding == true);
         }
 
+        private void RemoveAdorner(object? sender, PointerEventArgs e)
+        {
+            _adorner?.Dispose();
+            _adorner = null;
+        }
+
         protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
         {
             base.OnPropertyChanged(change);