Observe volume setting alongside broadcast event to faster react to the

volume changes

Broadcast queue is specially busy right after device boot. This change
mitigates this case.

Flag: com.android.systemui.new_volume_panel
Test: atest AudioRepositoryTest
Test: atest AudioVolumeInteractorTest
Test: manual on the phone
Bug: 341486445
Change-Id: I9cd146e2901a61a5887e07eae03d2a5447e1660b