CmdPal: Make it easier to add APIs in the future (#41056)

We learned a lot about adding interfaces in WinRT this week. I figured
I'd send a PR to write it all down.

src/modules/cmdpal/extensionsdk/Microsoft.CommandPalette.Extensions.Toolkit/IconData.cs

@@ -2,6 +2,7 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Diagnostics.CodeAnalysis;
 using Windows.Storage.Streams;
 
 namespace Microsoft.CommandPalette.Extensions.Toolkit;