Add ImsStateCallback

registerImsStateCallback and unregisterImsStateCallback are
added to ImsMmTelManager, ImsRcsManager, and SipDelegateManager.
Those are used to receive updates about the connection state
of the underlying ImsService.

Bug: 178016400
Test: atest ImsStateCallbackTest

Change-Id: If547ce637725d4f98942b0b554187a0ba91f60de
Merged-In: If547ce637725d4f98942b0b554187a0ba91f60de
Merged-In: I3ac14cc3bcb28f5f966a1b3c215727784527e475