Add Support for RPLMN to Voice and Data RegState

-Define RegistrationFailCause as an enum
-Combine voice and data reg state into a single struct
-Define a safe-union for AN-specific registration info

Bug: 73629308
Test: make && make VtsHalRadioV1_5TargetTest
      && make cf_x86_64_phone-userdebug

Change-Id: I43df3cffd4c55f2c5df8eaf0235772e5930dced5