Updating the APIs for the Callback Mode

This commit updates the APIs for the Callback Mode.
This includes System API updates.

Bug: 260533540
Bug: 359064059
Test: atest CtsTelephonyTestCases:TelephonyCallbackTest,
      atest CtsTelephonyTestCases:TelephonyRegistryManagerTest
Test: atest TelephonyRegistryTest, atest DefaultPhoneNotifierTest
Test: Manual call tests related to emergency and non-emergency calls.
Flag: com.android.internal.telephony.flags.emergency_callback_mode_notification

Change-Id: I2db870b796b5bef9e9ac7d232ee4b960ed27731e