Merge changes from topics "delegate_regi_new_state_losing_pdn", "ims_rcs_api_improvement_delegate_regi_state"

* changes:
  DelegateRegistrationState Improvement adding new states for DelegateRegistrationState:  - DEREGISTERING_REASON_LOSING_PDN  - DEREGISTERING_REASON_UNSPECIFIED
  IMS RCS API Improvements-DelegateRegistrationState