[core] fix memory leak with CarouselView & INotifyCollectionChanged

Context: dotnet#17726

In investigating dotnet#17726, I found a memory leak with `CarouselView`:

1. Have a long-lived `INotifyCollectionChanged` like
   `ObservableCollection`, that lives the life of the application.

2. Set `CarouselView.ItemsSource` to the collection.

3. `CarouselView` will live forever, even if the page is popped, etc.

I further expanded upon `MemoryTests` to assert more things for each
control, and was able to reproduce this issue.

To solve the problem, I used the same technique in 58a42e5. We can use
`WeakNotifyCollectionChangedProxy` in the `ObservableItemsSource` class
to prevent `CarouselView` from leaking. `ObservableItemsSource` is used
for other controls, so this may fix other leaks as well.

Unfortunately, this does not fully solve dotnet#17726, as there is at least
one further leak on Android from my testing.

src/Controls/src/Core/Handlers/Items/Android/ItemsSources/ItemsSourceFactory.cs

@@ -20,7 +20,7 @@ public static IItemsViewSource Create(IEnumerable itemsSource, BindableObject co
 				case IList list when itemsSource is INotifyCollectionChanged:
 					return new ObservableItemsSource(new MarshalingObservableCollection(list), container, notifier);
 				case IEnumerable _ when itemsSource is INotifyCollectionChanged:
-					return new ObservableItemsSource(itemsSource as IEnumerable, container, notifier);
+					return new ObservableItemsSource(itemsSource, container, notifier);
 				case IList list:
 					return new ListSource(list);
 				case IEnumerable<object> generic:

src/Controls/src/Core/Handlers/Items/Android/ItemsSources/ObservableItemsSource.cs

@@ -10,15 +10,19 @@ internal class ObservableItemsSource : IItemsViewSource, IObservableItemsViewSou
 		readonly IEnumerable _itemsSource;
 		readonly BindableObject _container;
 		readonly ICollectionChangedNotifier _notifier;
+		readonly WeakNotifyCollectionChangedProxy _proxy = new();
+		readonly NotifyCollectionChangedEventHandler _collectionChanged;
 		bool _disposed;
 
+		~ObservableItemsSource() => _proxy.Unsubscribe();
+
 		public ObservableItemsSource(IEnumerable itemSource, BindableObject container, ICollectionChangedNotifier notifier)
 		{
-			_itemsSource = itemSource as IList ?? itemSource as IEnumerable;
+			_itemsSource = itemSource;
 			_container = container;
 			_notifier = notifier;
-
-			((INotifyCollectionChanged)itemSource).CollectionChanged += CollectionChanged;
+			_collectionChanged = CollectionChanged;
+			_proxy.Subscribe((INotifyCollectionChanged)itemSource, _collectionChanged);
 		}
 
 

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

@@ -1,7 +1,9 @@
 using System;
+using System.Collections.ObjectModel;
 using System.Threading.Tasks;
 using Microsoft.Maui.Controls;
 using Microsoft.Maui.Controls.Handlers.Compatibility;
+using Microsoft.Maui.Controls.Handlers.Items;
 using Microsoft.Maui.Handlers;
 using Microsoft.Maui.Hosting;
 using Xunit;
@@ -18,6 +20,7 @@ void SetupBuilder()
 			builder.ConfigureMauiHandlers(handlers =>
 			{
 				handlers.AddHandler<Border, BorderHandler>();
+				handlers.AddHandler<CarouselView, CarouselViewHandler>();
 				handlers.AddHandler<CheckBox, CheckBoxHandler>();
 				handlers.AddHandler<DatePicker, DatePickerHandler>();
 				handlers.AddHandler<Entry, EntryHandler>();
@@ -38,6 +41,7 @@ void SetupBuilder()
 
 	[Theory("Handler Does Not Leak")]
 	[InlineData(typeof(Border))]
+	[InlineData(typeof(CarouselView))]
 	[InlineData(typeof(ContentView))]
 	[InlineData(typeof(CheckBox))]
 	[InlineData(typeof(DatePicker))]
@@ -65,11 +69,22 @@ public async Task HandlerDoesNotLeak(Type type)
 		WeakReference platformViewReference = null;
 		WeakReference handlerReference = null;
 
+		var observable = new ObservableCollection<int> { 1, 2, 3 };
+
 		await InvokeOnMainThreadAsync(() =>
 		{
 			var layout = new Grid();
 			var view = (View)Activator.CreateInstance(type);
 			layout.Add(view);
+			if (view is ContentView content)
+			{
+				content.Content = new Label();
+			}
+			else if (view is ItemsView items)
+			{
+				items.ItemTemplate = new DataTemplate(() => new Label());
+				items.ItemsSource = observable;
+			}
 			var handler = CreateHandler<LayoutHandler>(layout);
 			viewReference = new WeakReference(view);
 			handlerReference = new WeakReference(view.Handler);