Thread: Add ThreadBase_ThreadLoop capability

A virtual mutex to guard methods and variables that
only run on the single thread threadLoop().

Some additional thread-safety annotations are added.

Test: atest AudioTrackTest AudioRecordTest
Test: atest AAudioTests AudioTrackOffloadTest
Test: atest AudioPlaybackCaptureTest
Test: Camera YouTube
Bug: 275748373
Merged-In: I6fb87cc8d362c5ddd928563f193fd43f0d02a04c
Change-Id: I6fb87cc8d362c5ddd928563f193fd43f0d02a04c