Restructure registration API to allow for MMTEL and RCS to both manage registration callbacks as well as provide new query APIs for registration state and transport type. Bug: 122098288 Test: atest GtsTelephonyTestCases Merged-In: Ia568dcd059c2bcef26462e808088901edf6b072f Change-Id: Ia568dcd059c2bcef26462e808088901edf6b072f