Merge pull request unoplatform#15357 from ramezgerges/uielement_inval…

…idation_perf

perf: reduce layout invalidations when clearing children when there're none

src/Uno.UI/UI/Xaml/UIElement.skia.cs

@@ -206,6 +206,11 @@ internal UIElement ReplaceChild(int index, UIElement child)
 
 		internal void ClearChildren()
 		{
+			if (_children.Count == 0)
+			{
+				return;
+			}
+
 			foreach (var child in _children.ToArray())
 			{
 				InnerRemoveChild(child);

src/Uno.UI/UI/Xaml/UIElementCollection.cs

@@ -70,8 +70,10 @@ public void Clear()
 			// This block is a manual enumeration to avoid the foreach pattern
 			// See https://github.com/dotnet/runtime/issues/56309 for details
 			var itemsEnumerator = items.GetEnumerator();
+			var hasItems = false;
 			while (itemsEnumerator.MoveNext())
 			{
+				hasItems = true;
 				var item = itemsEnumerator.Current;
 
 				if (item is IDependencyObjectStoreProvider provider)
@@ -85,6 +87,11 @@ public void Clear()
 				fe.InvalidateMeasure();
 			}
 
+			if (!hasItems)
+			{
+				return;
+			}
+
 			OnCollectionChanged(new NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction.Remove, items.ToList()));
 		}