Revert "Fix hangs and NREs with Entry Observer (#14859)"

This reverts commit 5188c4f.

Xamarin.Forms.Platform.iOS/Renderers/EntryRenderer.cs

@@ -39,8 +39,8 @@ public abstract class EntryRendererBase<TControl> : ViewRenderer<Entry, TControl
 		bool _useLegacyColorManagement;
 
 		bool _disposed;
-		bool _observedSublayers;
 		IDisposable _selectedTextRangeObserver;
+		IDisposable _clearButtonSublayerObserver;
 		bool _nativeSelectionIsUpdating;
 
 		bool _cursorPositionChangePending;
@@ -93,12 +93,7 @@ protected override void Dispose(bool disposing)
 					Control.EditingDidEnd -= OnEditingEnded;
 					Control.ShouldChangeCharacters -= ShouldChangeCharacters;
 					_selectedTextRangeObserver?.Dispose();
-
-					if (_observedSublayers)
-					{
-						ClearButton?.Layer?.RemoveObserver(this, new NSString("sublayers"));
-						_observedSublayers = false;
-					}
+					_clearButtonSublayerObserver?.Dispose();
 				}
 			}
 
@@ -133,8 +128,7 @@ protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
 				textField.ShouldChangeCharacters += ShouldChangeCharacters;
 				_selectedTextRangeObserver = textField.AddObserver("selectedTextRange", NSKeyValueObservingOptions.New, UpdateCursorFromControl);
 
-				ClearButton?.Layer.AddObserver(this, new NSString("sublayers"), NSKeyValueObservingOptions.New, IntPtr.Zero);
-				_observedSublayers = true;
+				_clearButtonSublayerObserver = ClearButton?.Layer.AddObserver(new NSString("sublayers"), NSKeyValueObservingOptions.New, UpdateClearButtonSublayer);
 			}
 
 			// When we set the control text, it triggers the UpdateCursorFromControl event, which updates CursorPosition and SelectionLength;
@@ -166,12 +160,6 @@ protected override void OnElementChanged(ElementChangedEventArgs<Entry> e)
 				UpdateClearButtonVisibility();
 		}
 
-		public override void ObserveValue(NSString keyPath, NSObject ofObject, NSDictionary change, IntPtr context)
-		{
-			if (keyPath == new NSString("sublayers") && _defaultClearImage == null)
-				UpdateClearButtonVisibility();
-		}
-
 		protected override void OnElementPropertyChanged(object sender, PropertyChangedEventArgs e)
 		{
 			if (e.PropertyName == Entry.PlaceholderProperty.PropertyName || e.PropertyName == Entry.PlaceholderColorProperty.PropertyName)
@@ -446,6 +434,15 @@ void UpdateCursorFromControl(NSObservedChange obj)
 			}
 		}
 
+		void UpdateClearButtonSublayer(NSObservedChange obj)
+		{
+			if (Control == null || Element == null)
+				return;
+
+			if (_defaultClearImage == null)
+				UpdateClearButtonVisibility();
+		}
+
 		void UpdateCursorSelection()
 		{
 			if (_nativeSelectionIsUpdating || Control == null || Element == null)