Update EmergencyStateTracker to cover emergency SMS and edge cases

This CL contains the followings:
 - Adds emergency SMS APIs: startEmergencySms/endSms
 - Covers some edge cases:
   - Waits for ongoing call/SMS before the emergency mode is exited if
     an emergency call/SMS ends while another emergency call/SMS is in
     progress on the same phone.
   - Basically, an emergency call will be handled with priority, and if
     an emergency call/SMS starts on the same or different phone
     sequentially, it will be processed with a proper manner by
     canceling and proceeding or returning the result immediately.

Bug: 267220850
Test: atest EmergencyStateTrackerTest
Test: manual (verify emergency call/SMS start/end with test emergency number)
Change-Id: I46980424ce735df149fcc6166f24785a060d6bc0