Add wrapper for AudioDeviceVolumeManager in the HDMI framework

Adding a wrapper interface for AudioDeviceVolumeManager allows the class
to be faked. This allows tests that instantiate HdmiControlService to
avoid also instantiating AudioDeviceVolumeManager, which can affect the
state of AudioService on the DUT.

Using an interface instead of inheritance allows constructors to be more
independent, and allows the same class to "wrap" multiple managers in
the future if they need to share state (e.g. AudioManager and
AudioDeviceVolumeManager).

Bug: 217923086
Test: atest com.android.server.hdmi
Change-Id: I673ab6e3a6acbbc6af8998e2f5c048fec59ad47a