fix: Avoid propagating FindName to Content if ContentTemplate is used

Currently we were propagating FindName to the Content view, even if it was "overriden" by the ContentTemplate, which then could result in StackOverflow

src/Uno.UI/UI/Xaml/IFrameworkElement.cs

@@ -255,9 +255,17 @@ public static IFrameworkElement FindName(IFrameworkElement e, ViewGroup group, s
 
 			// If element is a ContentControl with a view as Content, include the view and its children in the search,
 			// to better match Windows behaviour
-			var content =
-				(e as ContentControl)?.Content as IFrameworkElement ??
-				(e as Controls.Primitives.Popup)?.Child as IFrameworkElement;
+			IFrameworkElement content = null;
+			if (e is ContentControl contentControl &&
+				contentControl.Content is IFrameworkElement innerContent &&
+				contentControl.ContentTemplate is null) // Only include the Content view if there is no ContentTemplate.
+			{
+				content = innerContent;
+			}
+			else if (e is Controls.Primitives.Popup popup)
+			{
+				content = popup.Child as IFrameworkElement;
+			}
 
 			if (content != null)
 			{