TimeCheck: Track waiting through thread join in AudioFlinger

The TimeCheck watchdog is used to diagnose binder stalls.
When one occurs, it does a thread-wait analysis, tracking
downstream to the ultimate thread the target is blocked on.

We add thread join diagnostic tracing in AudioFlinger
ThreadBase::exit().

Test: atest CtsMediaAudioTestCases
Bug: 328693634
Merged-In: Id633d1371c6aedd111a04510c49e95729a0c7790
Change-Id: Id633d1371c6aedd111a04510c49e95729a0c7790