audio: Implement OnSessionStarted for HAL 2.1 am: a80a851ada am: 81624c5ef7 am: 2f667a0384 am: f28eec7ad1

Original change: https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1608075

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: If5664578ff0a45ea602721fae90028d499af26a5