[windows] fix memory leak in TabbedPage

Context: dotnet#23166

This expands upon dotnet#23166 (iOS/Catalyst memory leaks for `TabbedPage`),
fixing the same problem on Windows. I could reproduce the problem in
`MemoryTests.cs`.

I found the `NavigationViewItemViewModel.Data` property held the
`ContentPage` that held onto the `TabbedPage`. I made the backing field
a `WeakReference` and the test in `MemoryTests.cs` now passes on Windows.

src/Controls/tests/DeviceTests/Memory/MemoryTests.cs

@@ -76,18 +76,9 @@ void SetupBuilder()
 	[InlineData(typeof(TabbedPage))]
 	public async Task PagesDoNotLeak(Type type)
 	{
-#if WINDOWS
-		// FIXME: there is still an issue with TabbedPage on Windows
-		if (type == typeof(TabbedPage))
-			return;
-#endif
-
 		SetupBuilder();
 
-		WeakReference viewReference = null;
-		WeakReference handlerReference = null;
-		WeakReference platformViewReference = null;
-
+		var references = new List<WeakReference>();
 		var navPage = new NavigationPage(new ContentPage { Title = "Page 1" });
 
 		await CreateHandlerAndAddToWindow(new Window(navPage), async () =>
@@ -111,16 +102,22 @@ await CreateHandlerAndAddToWindow(new Window(navPage), async () =>
 			
 			await navPage.Navigation.PushModalAsync(page);
 
-			viewReference = new WeakReference(page);
-			handlerReference = new WeakReference(page.Handler);
-			platformViewReference = new WeakReference(page.Handler.PlatformView);
+			references.Add(new(page));
+			references.Add(new(page.Handler));
+			references.Add(new(page.Handler.PlatformView));
 
-			// Windows requires Loaded event to fire before unloading
 			await OnLoadedAsync(pageToWaitFor);
+			if (pageToWaitFor != page)
+			{
+				references.Add(new(pageToWaitFor));
+				references.Add(new(pageToWaitFor.Handler));
+				references.Add(new(pageToWaitFor.Handler.PlatformView));
+			}
+
 			await navPage.Navigation.PopModalAsync();
 		});
 
-		await AssertionExtensions.WaitForGC(viewReference, handlerReference, platformViewReference);
+		await AssertionExtensions.WaitForGC(references.ToArray());
 	}
 
 	[Theory("Handler Does Not Leak")]

src/Core/src/Platform/Windows/NavigationViewItemViewModel.cs

@@ -89,6 +89,7 @@ internal class NavigationViewItemViewModel : INotifyPropertyChanged
 		WBrush? _unselectedForeground;
 		ObservableCollection<NavigationViewItemViewModel>? _menuItemsSource;
 		WIconElement? _icon;
+		WeakReference<object>? _data;
 
 		public object? Content
 		{
@@ -112,7 +113,11 @@ public WBrush? Background
 			get => IsSelected ? SelectedBackground : UnselectedBackground;
 		}
 
-		public object? Data { get; set; }
+		public object? Data
+		{
+			get => _data?.GetTargetOrDefault();
+			set => _data = value is null ? null : new(value);
+		}
 
 		public ObservableCollection<NavigationViewItemViewModel>? MenuItemsSource
 		{