Border inside a frame fix (#18526)

src/Controls/src/Core/Border/Border.cs

@@ -64,6 +64,12 @@ void NotifyStrokeShapeChanges()
 
 			if (strokeShape is VisualElement visualElement)
 			{
+				// By setting visibility to false, the shape is not
+				// considered when calculating the size of its container, but can
+				// still be accessed as a children. In the context of
+				// border the IsVisible property of shape is not used.
+				visualElement.IsVisible = false;
+
 				AddLogicalChild(visualElement);
 				_strokeShapeChanged ??= (sender, e) => OnPropertyChanged(nameof(StrokeShape));
 				_strokeShapeProxy ??= new();