aaudio: fix CTS for MMAP mode

Improve calculation of buffer capacity based on requested minimum.
Adjust timing of start() to reduce underflows.
Track ServiceEndpoints based on requested deviceId.
Fix getFramesRead() and flush() behavior.
Fix timeouts due to ClockModel lateness bug.
Misc cleanup.

Bug: 37755299
Test: test_aaudio.cpp
Change-Id: I637c16e87fbe14b6f28c60aeea0b9dfed965ecd0
diff --git a/services/oboeservice/AAudioServiceEndpointPlay.h b/services/oboeservice/AAudioServiceEndpointPlay.h
index b977960..89935ae 100644
--- a/services/oboeservice/AAudioServiceEndpointPlay.h
+++ b/services/oboeservice/AAudioServiceEndpointPlay.h
@@ -32,6 +32,9 @@
 
 namespace aaudio {
 
+/**
+ * Contains a mixer and a stream for writing the result of the mix.
+ */
 class AAudioServiceEndpointPlay : public AAudioServiceEndpoint {
 public:
     explicit AAudioServiceEndpointPlay(android::AAudioService &audioService);