floss: avrcp: add a few DBUS methods for media information

Add a few DBUS methods under the Floss media interface to receive media
information propagated from Chrome CRAS. This is a temporary solution
to expedite the AVRCP implementation, and the interface are subjected
to change once Chrome CRAS is bypassed for media information-related
calls.

Bug: 240780471
Tag: #floss
Test: local print out verified DBUS call received

Change-Id: I6cc57139489575b59a71bce155cebd0a5b95d385