Spatializer: process callbacks in separate thread

Add a Looper and Handler to process events from the engine
and pose controler callback to avoid cross mutex deadlocks.

Bug: 188502620
Test: manual test with mock spatializer
Change-Id: I1342602259b147727c704ad7bbeb1b3a68c7b231
Merged-In: I1342602259b147727c704ad7bbeb1b3a68c7b231
3 files changed