Change session ID string to ID object

Based on API review feedback from jmtrivi@ to reduce unexpected
usage of the APIs.

And add some stub APIs

Reference CLs:
MediaDrm ag/13835091 by robertshih@
MediaExtractor: ag/13607751 by aquilescanta@
MediaParser: ag/13714647 by aquilescanta@
MediaRecorder: ag/13545885 by dichenzhang@
AudioTrack & AudioRecord: ag/13712857 by hunga@

Bug: 183095725
Test: pending CTS
CTS-Coverage-Bug: 183366721
Change-Id: I931edf021a5ec6b27a25bc6142a129b92da0fc9a