Ensure containers show up in the menu when they are created

Toolkit.UI.Controls.Avalonia/Class1.cs

@@ -0,0 +1,17 @@
+using Avalonia.Controls;
+using Avalonia.Controls.Primitives;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Toolkit.UI.Controls;
+
+public class AttachedFlyout : PopupFlyoutBase
+{
+    protected override Control CreatePresenter()
+    {
+        throw new NotImplementedException();
+    }
+}