android: rework aout device/stream + add AAudio

Previously submitted on December: https://mailman.videolan.org/pipermail/vlc-devel/2020-December/140691.html + https://mailman.videolan.org/pipermail/vlc-devel/2020-December/140762.html

It's a draft since the audio startup is glitchy: frames drop when audio is the master, or a lot of flush/resample. The correct fix may belong to VLC core, in the clock part, probably output jitter handling.