remove notification manager property from toplevel. remove unused notification manager in control catalog main window

samples/ControlCatalog/MainWindow.xaml.cs

@@ -11,23 +11,13 @@ namespace ControlCatalog
 {
     public class MainWindow : Window
     {
-        private WindowNotificationManager _notificationArea;
         private NativeMenu? _recentMenu;
 
         public MainWindow()
         {
             this.InitializeComponent();
 
-            //Renderer.DrawFps = true;
-            //Renderer.DrawDirtyRects = Renderer.DrawFps = true;
-
-            _notificationArea = new WindowNotificationManager(this)
-            {
-                Position = NotificationPosition.TopRight,
-                MaxItems = 3
-            };
-
-            DataContext = new MainWindowViewModel(_notificationArea);
+            DataContext = new MainWindowViewModel();
             _recentMenu = ((NativeMenu.GetMenu(this)?.Items[0] as NativeMenuItem)?.Menu?.Items[2] as NativeMenuItem)?.Menu;
         }
 

samples/ControlCatalog/Pages/NotificationsPage.xaml.cs

@@ -27,7 +27,7 @@ namespace ControlCatalog.Pages
         {
             base.OnAttachedToVisualTree(e);
 
-            _viewModel.NotificationManager = (VisualRoot as TopLevel)?.NotificationManager;
+            _viewModel.NotificationManager = new Avalonia.Controls.Notifications.WindowNotificationManager(VisualRoot as TopLevel);
         }
     }
 }

samples/ControlCatalog/ViewModels/MainWindowViewModel.cs

@@ -24,7 +24,7 @@ namespace ControlCatalog.ViewModels
         private bool _preferSystemChromeEnabled;
         private double _titleBarHeight;
 
-        public MainWindowViewModel(IManagedNotificationManager notificationManager)
+        public MainWindowViewModel()
         {
             AboutCommand = MiniCommand.CreateFromTask(async () =>
             {

src/Avalonia.Controls/Notifications/WindowNotificationManager.cs

@@ -54,20 +54,12 @@ namespace Avalonia.Controls.Notifications
         /// Initializes a new instance of the <see cref="WindowNotificationManager"/> class.
         /// </summary>
         /// <param name="host">The window that will host the control.</param>
-        public WindowNotificationManager(TopLevel host)
+        public WindowNotificationManager(TopLevel? host)
         {
-            if (VisualChildren.Count != 0)
+            if (host != null)
             {
                 Install(host);
             }
-            else
-            {
-                Observable.FromEventPattern<TemplateAppliedEventArgs>(host, nameof(host.TemplateApplied)).Take(1)
-                    .Subscribe(_ =>
-                    {
-                        Install(host);
-                    });
-            }
 
             UpdatePseudoClasses(Position);
         }

src/Avalonia.Controls/TopLevel.cs

@@ -96,7 +96,6 @@ namespace Avalonia.Controls
         private Border? _transparencyFallbackBorder;
         private TargetWeakEventSubscriber<TopLevel, ResourcesChangedEventArgs>? _resourcesChangesSubscriber;
         private IStorageProvider? _storageProvider;
-        private WindowNotificationManager? _notificationManager;
         
         /// <summary>
         /// Initializes static members of the <see cref="TopLevel"/> class.
@@ -330,18 +329,6 @@ namespace Avalonia.Controls
 
         IRenderTarget IRenderRoot.CreateRenderTarget() => CreateRenderTarget();
 
-        public WindowNotificationManager NotificationManager
-        {
-            get
-            {
-                if(_notificationManager == null)
-                {
-                    _notificationManager = new WindowNotificationManager(this);
-                }
-                return _notificationManager;
-            }
-        }
-
         /// <inheritdoc/>
         protected virtual IRenderTarget CreateRenderTarget()
         {