Add CTS test for onCarrierRoamingNtnSignalStrengthChanged callback. Bug: 350396906 Test: atest TelephonyRegistryManagerTest, TelephonyCallbackTest, Test: Manually tested SMS/MMS/CALLS/DATA Flag: com.android.internal.telephony.flags.carrier_roaming_nb_iot_ntn Change-Id: I481a70a8d9ea0b13988deae7f77e05362e55dab3