AudioVolumeGroup introspection & callback JAVA APIs

This CL adds introspection APIs for Audio Volume group
and callback notification on group volume change.
It allows to keep the same level of service available today
in CarAudioManager and is a starting point to get rid of Stream Alias
hard coded in AudioServer.

Bug: 124767636
Test: dumpsys media.audio_policy
Change-Id: I48909df93c146f071acd24cd3ecc608cb98b4d7e
Signed-off-by: François Gaffie <francois.gaffie@renault.com>