New APIs for immersive audio

- AudioManager: entry point for getting
 a Spatializer object, if supported
- Spatializer: entry point for spatializer
 capabilities, system APIs for configuration
 and compatibility with devices
- AudioAttributes: additions for behavior of
 a track for virtualization

Bug: 191404931
Test: atest AudioAttributesTest SpatializerTest
Change-Id: I06f8acdd979f8d4374042f8209082c79f49a1f75