Update ReactiveUI Example

ReactiveExample/ViewExtensions.cs

@@ -0,0 +1,24 @@
+using System;
+using Terminal.Gui;
+
+namespace ReactiveExample;
+public static class ViewExtensions
+{
+    public static (Window MainView, TOut LastControl) AddControl<TOut> (this Window view, Action<TOut> action)
+        where TOut : View, new()
+    {
+        TOut result = new ();
+        action (result);
+        view.Add (result);
+        return (view, result);
+    }
+
+    public static (Window MainView, TOut LastControl) AddControlAfter<TOut> (this (Window MainView, View LastControl) view, Action<View, TOut> action)
+        where TOut : View, new()
+    {
+        TOut result = new ();
+        action (view.LastControl, result);
+        view.MainView.Add (result);
+        return (view.MainView, result);
+    }
+}