AudioManager.getSpatializer() never returns null

Spatializer instance returned by AudioManager.getSpatializer()
 is never null.
Instead of having this getter return null when the device
 doesn't support spatialization, the user can query the
 instance for it's level of support for the feature.
The level of support is independent of the state of the
 spatializer.

Bug: 191404931
Test: atest SpatializerTest
Change-Id: Id08670749b4d34230313d2cd829aa5ba414dae21