MediaPlayerUI with MPV Support

[mysteryx93]

I think that a decent media player for Avalonia is overdue, so here it is: MPV implementation with OpenGL support with standard player user interface
https://github.com/mysteryx93/MediaPlayerUI.NET
https://www.nuget.org/packages/MediaPlayer.Avalonia.Mpv/2.0.0-rc1

It's not perfect, but it's working. TODO list for improvements is here.