Add onCarrierRoamingNtnSignalStrengthChanged callback.

Bug: 377030018
Test: atest TelephonyCallbackTest, atest TelephonyRegistryManagerTest
FLAG: com.android.internal.telephony.flags.carrier_roaming_nb_iot_ntn
Change-Id: I8a84a6aef82baa463c2ba94bc0295d47c1fb8df5
6 files changed