Move MediaBrowserService to Bluetooth Process

MediaBrowserService exports A2DP streaming features to the rest of stack
using the MediaBrowser API. Currently it was being stareted by
BOOT_COMPLETE which made it start very late. Also that meant that some
of the broadcasts for the connection events is lost. Now it is started
by the A2DP state machine so that we do not miss any state changes.

Bug: 27744764
Change-Id: I193b4adfea09cbd90e41f1a217383b6aa234ef2b