Updating the APIs for the emergency callback mode

This commit updates the APIs for the emergency callback mode.
This includes an updated implementation of TelephonyCallback.

Bug: 260533540
Bug: 359064059
Test: atest CtsTelephonyTestCases:TelephonyCallbackTest,
      atest CtsTelephonyTestCases:TelephonyRegistryManagerTest
Test: atest TelephonyRegistryTest, atest DefaultPhoneNotifierTest
Flag: com.android.internal.telephony.flags.emergency_callback_mode_notification

Change-Id: I60a4d1c080a39571cc939cee1448673b36895795