chore: change border to FrameworkElement

src/AddIns/Uno.UI.MediaPlayer.Skia.Gtk/GTKMediaPlayer.cs

@@ -28,7 +28,7 @@ using Windows.Media.Core;
 
 namespace Uno.UI.Media;
 
-public partial class GtkMediaPlayer : Border
+public partial class GtkMediaPlayer : FrameworkElement
 {
 	private LibVLC? _libvlc;
 	private LibVLCSharp.Shared.MediaPlayer? _mediaPlayer;

src/AddIns/Uno.UI.MediaPlayer.Skia.Gtk/GTKMediaPlayer.events.cs

@@ -72,8 +72,8 @@ public partial class GtkMediaPlayer
 			_mediaPlayer.Stopped += OnMediaPlayerStopped;
 
 			_videoContainer.Content = _videoView;
-
-			Child = _videoContainer;
+			AddChild(_videoContainer);
+			//Child = _videoContainer;
 
 			UpdateVideoStretch();
 			if (this.Log().IsEnabled(Microsoft.Extensions.Logging.LogLevel.Debug))