[FR] Add AirPlay 2 output support

[kode54]

Describe This can be implemented on 10.15 and newer using:

https://developer.apple.com/documentation/avfoundation/media_playback_and_selection/getting_airplay_2_into_your_app

I'll look into what it takes to get a separate AirPlay 2 output module working, which will only be remembered for the life of the app, or until the user disables it. User requested it as a main window button similar to Apple Music.