AudioService: initialize Spatializer, track routing changes

Implement initialization of SpatializerHelper, the AudioService
 proxy for the native Spatializer effect.
Implement release of Spatializer effect when feature is disabled
Implement Spatializer available dispatch.
Track routing changes reported through AudioSystem to
 check if device for media routing is compatible with
 spatialization. Use result to update Spatializer
 availability

Bug: 188502620
Test: adb logcat | grep Spatializer, check for "init succeeded"
Change-Id: Ib06b1f54fee20a5057768a7a31a047bd1fba930d