Reland "Expose GenericSoundModel as SystemApi."

API-Coverage-Bug:342000786

Bug: 339267254
Flag: android.media.soundtrigger.generic_model_api
Test: Successfully load the generic sound model and verify
      sound trigger event could be triggered correctly on
      Pixel Watch devices.
Change-Id: Ifbd30375933d0d87426db7614614a84cde787ae8