Bug 5045498 Force display update when display registers

When an IRemoteControlDisplay registers, cause the
 RemoteControlClient to send all its information to the newly
 registered display.
The previous code was only sending a request for update: this
 request didn't here cause the client to send the data because
 a new client generation had not been synchronized among clients
 and displays.
This CL uses the same code path to force an update as when audio
 focus changes, or a new client registers, by calling the same
 method that is called in those cases,
 updateRemoteControlDisplay_syncRcs(flags).
Also in this CL: more method renames to indicate methods that
 are called synchronized on mRCStack.

Change-Id: I54102f45ba1cd4812d958ecd883bec7bc45ae88f