Controls, Startup&Driver improvements

src/Library/TerminalUI/Extensions/ViewExtensions.cs

@@ -0,0 +1,14 @@
+using TerminalUI.Controls;
+
+namespace TerminalUI.Extensions;
+
+public static class ViewExtensions
+{
+    public static T? GetExtension<T>(this IView view)
+        => (T?) view.Extensions.FirstOrDefault(e => e is T);
+
+    public static ChildWithDataContextMapper<TSourceDataContext, TTargetDataContext> WithDataContextMapper<TSourceDataContext, TTargetDataContext>(
+        this IView<TTargetDataContext> view,
+        Func<TSourceDataContext?, TTargetDataContext?> dataContextMapper)
+        => new(view, dataContextMapper);
+}