Spatializer: add output changed method on native callback

Add onOutputChanged() method to INativeSpatializerCallback
indicating when the output stream the Spatializer is attached to
changes.

Test: run and enable/disable spatial audio
Bug: 202723925
Change-Id: I5f7c5e0038f1c9235ee6fcdd0b56b7f2af07e01a
2 files changed