Improve HdmiControlManager#getActiveSource

Make HdmiControlManager#getActiveSource return better results on
Playback devices by fetching the active source from the list of known
devices in the HDMI-CEC network.

Bug: 166227491
Test: atest com.android.server.hdmi
Change-Id: I0cfaf1d857e11a222af118b56337fb5f378b70ef
3 files changed