Support for Uno platform (WinUI3)

[jp-weber]

I would be very happy if the extension would also work for a project based on uno platform. this would then also support WinUI3 through the namespace.

In order to keep this compatible with UWP, we could set a condition (C#):

using System;
using Windows.ApplicationModel.Resources;
#if WINDOWS_UWP
using Windows.UI.Xaml.Markup;
using Windows.UI.Xaml.Data;
#else
using Microsoft.UI.Xaml.Markup;
using Microsoft.UI.Xaml.Data;
#endif