Add DropDownListExample scenario with MenuBar usage

Simple prototype for now

Examples/UICatalog/Scenarios/DropDownListExample.cs

@@ -0,0 +1,57 @@
+#nullable enable
+
+namespace UICatalog.Scenarios;
+
+[ScenarioMetadata ("DropDownListExample", "Shows how to use MenuBar as a Drop Down List")]
+[ScenarioCategory ("Controls")]
+public sealed class DropDownListExample : Scenario
+{
+    public override void Main ()
+    {
+        // Init
+        Application.Init ();
+
+        // Setup - Create a top-level application window and configure it.
+        Window appWindow = new ()
+        {
+            Title = GetQuitKeyAndName (),
+            BorderStyle = LineStyle.None
+        };
+
+        Label l = new Label () { Title = "_DropDown:" };
+
+        TextField tf = new () { X = Pos.Right(l), Width = 10 };
+
+        MenuBarItem? menuBarItem  = new ($"{Glyphs.DownArrow}",
+                                Enumerable.Range (1, 5)
+                                          .Select (selector: i => new MenuItem($"item {i}", null, null, null) )
+                                          .ToArray ());
+
+        var mb = new MenuBar ([menuBarItem])
+        {
+            CanFocus = true,
+            Width = 1,
+            Y = Pos.Top (tf),
+            X = Pos.Right (tf)
+        };
+
+        // HACKS required to make this work:
+        mb.Accepted += (s, e) => {
+                        // BUG: This does not select menu item 0
+                        // Instead what happens is the first keystroke the user presses
+                        // gets swallowed and focus is moved to 0.  Result is that you have
+                        // to press down arrow twice to select first menu item and/or have to
+                        // press Tab twice to move focus back to TextField
+                        mb.OpenMenu ();
+                    };
+
+        appWindow.Add (l, tf, mb);
+
+        // Run - Start the application.
+        Application.Run (appWindow);
+        appWindow.Dispose ();
+
+        // Shutdown - Calling Application.Shutdown is required.
+        Application.Shutdown ();
+    }
+}