Improve permission enforcement in SoundTriggerService

Use a session-based identity mechanism similar to SoundTriggerMiddleware.
Clear identity context within service to allow internal calls to
originate from this service.

Fixes: 184021066
Test: Manual verification of OKG / Now Playing on Sargo
Change-Id: Iccda9ef864f82eafbf3473e706bcffe695705953
(cherry picked from commit def517ec0490530bc6a56b34318c5ee1a6f33e9e)
1 file changed