Multi-core support

[extreamsd]

After implementing multi-core processing support in my audio app on iOS, implementing it on Android turned out to be problematic.
In iOS, one can create real-time threads and join the real-time threads to an Audio Workgroup:
https://developer.apple.com/documentation/audiotoolbox/workgroup_management/understanding_audio_workgroups?language=objc

On Android, you cannot create additional real-time threads, so at most you can create some threads with prio -20. Unfortunately, sched_setaffinity() to fix a thread on a core does not work on the majority of Android devices. So this leads to the additional threads often just waiting on each other because they are placed on the same core. It does not matter if the performance cores are chosen or not.

It would be nice if Android/Oboe would provide features to be able to do proper multi-core processing for audio.