Seperated ambient mute state for different devices

In previous design, we'll sync the remote devices' mute states from the
phone side since we only have one icon to control them. However, there's
a user need to have seperated mute states. As a short term solution,
we update the behavior as followings:

1. Respect remote devices' mute states without any synchronization from
   phone side
2. Show the muted icon only when both devices are muted
3. If remote mute states are different, expand the controls to let user
   clearly know which device is muted by setting the slider to minimum
   value
4. Clicking on the volume icon will mute/unmute both devices as before

Flag: EXEMPT bugfix
Bug: 412968925
Test: manually test with real devices
Test: atest AmbientVolumeUiControllerTest
Change-Id: I7d45bf7daad6b105cc61c40d57192983977b0275