Allow dialer to play incoming call ringtone

This CL allows the default dialer app to play the incoming call
ringtone. This is useful because:
  - the sound will now be played at the same time the UI is shown.
    Previously the sound could be played earlier
  - it will be easier for the system to respect the user's do not
    disturb setting on a per contact basis

The dialer app can opt into the new behavior by setting a meta-data
value of IN_CALL_SERVICE_RINGING to true.

This CL also notifies the InCallService if silenceRinger was called.

BUG: 22857261
Change-Id: If1d05a922dd9869bc5b58157c67e9144001ee1ad