Tracking legacy remote submix active or not in RecordingActivityMonitor.

When enabling Live Caption, remote submix device will be set as fixed
and full volume device in audio service. In that case, volume control
for remote submix will not be forwarded anymore. However, it is expected
to have volume control when the device is on chromecast mirror mode.
To solve the problem, tracking legacy remote submix device is active or
not in RecordingActivityMonitor. When legacy remote submix device is
active, remote submix will not be treated as fixed/full volume device.
In audio policy manager, the remote submix that is used by dynamic
policy will still be fixed volume device.

Bug: 144063329
Test: repo steps in bug
Change-Id: I1cb83c17f34e636763bb989e37ac8e021217cc39