[controls] fix memory leak with CarouselView & INotifyCollectionChanged (#18267)

Context: #17726

In investigating #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 fully solve this, I had to fix issues on each platform.

~~ Android ~~

`ObservableItemsSource` subscribes to the `INotifyCollectionChanged`
event, making it live forever in this case.

To fix this, I used the same technique in 58a42e5:
`WeakNotifyCollectionChangedProxy`. `ObservableItemsSource` is used for
`ItemsView`-like controls, so this may fix other leaks as well.

~~ Windows ~~

Windows has the same issue as Android, but for the following types:

* `CarouselViewHandler` subscribes to `INotifyCollectionChanged`

* `ObservableItemTemplateCollection` subscribes to
  `INotifyCollectionChanged`

These could be fixed with `WeakNotifyCollectionChangedProxy`.

Then I found another issue with `ItemTemplateContext`

These three types are used for other `ItemsView`-like controls, so this
may fix other leaks as well.

~~ iOS/Catalyst ~~

These platforms suffered from multiple circular references:

* `CarouselViewController` -> `CarouselView` -> `CarouselViewHandler` ->
  `CarouselViewController`

* `ItemsViewController` -> `CarouselView` -> `CarouselViewHandler` ->
  `ItemsViewController` (`CarouselViewController` subclasses this)

* `CarouselViewLayout` -> `CarouselView` -> `CarouselViewHandler` ->
  `CarouselViewLayout`

The analyzer added in 2e65626 did not yet catch these because I only
added the analyzer so far for `Microsoft.Maui.dll` and these issues were
in `Microsoft.Maui.Controls.dll`. In a future PR, we can proactively try
to add the analyzer to all projects.

~~ Conclusion ~~

Unfortunately, this does not fully solve #17726, as there is at least
one further leak on Android from my testing. But this is a good step
forward.

Author: jonathanpeppers

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/src/Core/Handlers/Items/CarouselViewHandler.Windows.cs

@@ -23,6 +23,10 @@ public partial class CarouselViewHandler : ItemsViewHandler<CarouselView>
 		WScrollBarVisibility? _horizontalScrollBarVisibilityWithoutLoop;
 		WScrollBarVisibility? _verticalScrollBarVisibilityWithoutLoop;
 		Size _currentSize;
+		NotifyCollectionChangedEventHandler _collectionChanged;
+		readonly WeakNotifyCollectionChangedProxy _proxy = new();
+
+		~CarouselViewHandler() => _proxy.Unsubscribe();
 
 		protected override IItemsLayout Layout { get; }
 
@@ -47,9 +51,7 @@ protected override void DisconnectHandler(ListViewBase platformView)
 			if (ListViewBase != null)
 			{
 				ListViewBase.SizeChanged -= OnListViewSizeChanged;
-
-				if (CollectionViewSource?.Source is ObservableItemTemplateCollection observableItemsSource)
-					observableItemsSource.CollectionChanged -= OnCollectionItemsSourceChanged;
+				_proxy.Unsubscribe();
 			}
 
 			if (_scrollViewer != null)
@@ -120,7 +122,10 @@ protected override CollectionViewSource CreateCollectionViewSource()
 				GetItemHeight(), GetItemWidth(), GetItemSpacing(), MauiContext);
 
 			if (collectionViewSource is ObservableItemTemplateCollection observableItemsSource)
-				observableItemsSource.CollectionChanged += OnCollectionItemsSourceChanged;
+			{
+				_collectionChanged ??= OnCollectionItemsSourceChanged;
+				_proxy.Subscribe(observableItemsSource, _collectionChanged);
+			}
 
 			return new CollectionViewSource
 			{