Creates com.android.car.audio package

Foresee there will be more audio specific classes, and it's better
having them in a dedicated package.

CarAudioService is moved to audio package as well. Comments are added to
the public classes / interfaces to comply with the lint check (and it's
a good practice doing so).

Bug: 113051081
Test: m -j
Change-Id: I1fa9886f651f253f1a285d0f50be504808acd6e4
6 files changed