The audio regulator assumed a continuous audio stream. But some audio
sources (like the "voice call" audio source) do not produce any packets
on silence, breaking this assumption.
Use PTS to detect such discontinuities.
PR #5870 <https://github.com/Genymobile/scrcpy/pull/5870>
The audio player had 2 roles:
- handle the SDL audio output device;
- resample input samples to maintain a target latency.
Extract the latter to a separate component (an "audio regulator"),
independent of SDL.
