Add article, code projects, toc, and redirects (#1178)

Co-authored-by: Andy (Steve) De George <[email protected]>

dotnet-desktop-guide/net/wpf/properties/snippets/attached-properties-overview/csharp/App.xaml.cs

@@ -0,0 +1,11 @@
+using System.Windows;
+
+namespace CodeSampleCsharp
+{
+    /// <summary>
+    /// Interaction logic for App.xaml
+    /// </summary>
+    public partial class App : Application
+    {
+    }
+}