Request current track metadata when BIP connects

AVRCP Targets are not supposed to give image handles over with metadata
until an AVRCP BIP client connects from a particular controller. Because
this connection can happen any time and there's nothing forcing a target
to send us a track changed notification to inform us of the new handle,
the best thing we can do to work with all devices is to request it when
we connect on BIP. Otherwise, we risk a race condition between the BIP
connection and any amount of track changed notifications that might
happen organically.

This change, paired with one in /system/bt/, adds a method to the native
interface to allow us to request for current track metadata whenever we
want. We then call it when we learn of a BIP client connection.

Bug: 152655644
Test: Build, flash, atest
Change-Id: Ife75cd08a3affe1cc14a4254d1896c4299114f9f
Merged-In: Ife75cd08a3affe1cc14a4254d1896c4299114f9f