Add a WinUI3 look

[zenith391]

Due to the way WinUI 3 is designed and due to the fact that it has no C ABI interface available for it, I don't think using it directly is doable.

What can be done however is to render it with the win32 backend while somehow keeping accessibility support.

This could be done with open-sourced WPF data which includes stylesheets for every Windows theme or just use https://github.com/lepoco/wpfui/tree/main/src/Wpf.Ui/Styles

Another interesting resource is https://github.com/lepoco/wpfui which ports Fluent design to simple XAML style files.

If it's done, it would be interesting to offer it windowlessly (with the gles/webgpu/something else backend?) so that it's not bound by the same 10,000 handles limit as win32.

Another interesting perspective is how to support having one executable with modern Windows UI while still having the option to fallback to win32, but is this even a necessary use case? You can certainly ship two executables in this case.