this patch aim to allow setting the volume per player when mmdevice backend is used
the original issue is that if you spawn multiple libvlc player in a program, calling libvlc_audio_set_volume will set the volume for all instances rather than only the given player. The feature remains optional as we certainly want to keep the current behavior for VLC as a player(same volume in the app and in windows mixer)
the patch is greatly inspired from the work from @tguillem here https://patches.videolan.org/patch/20354/