aaudio: call stop() from the callback

Stop the stream when the callback returns AAUDIO_CALLBACK_RESULT_STOP.

Refactor start/pause/stop code to allow different paths for
stop from the app or from the callback.
Fix error handling in joinThread().
Simplify code path through PlayerBase.

Bug: 120932593
Bug: 121158739
Test: test_return_stop
Test: test_return_stop -i
Test: test_return_stop    -n
Test: test_return_stop -i -n
Test: atest CtsNativeMediaAAudioTestCases
Change-Id: I85134211348b26077693d9a71bf1331dad60da38