Add loading state in the MediaOutputViewModel

We need to distinguish between loading and null session in the
MediaOutputViewModel to wait for the initial load to finish.

Flag: aconfig new_volume_panel TRUNKFOOD
Test: manual on the phone
Fixes: 332721662
Change-Id: Ib9eb6cdade98fdd75ccacbac7b49caa782ba8bd6
2 files changed