Add Emergency Number Test Mode

Updatable emergency number test mode in EmergencyNumberTracker to support
add, remove, clear operations

Do not send emergency number in the test mode to the emergency dial.

Test: Treehugger
Bug: 122840137
Merged-in: I45fb6a94e4ff1ae789b6f96cdd6e74583c69b06e
Change-Id: I45fb6a94e4ff1ae789b6f96cdd6e74583c69b06e
(cherry picked from commit fe010584)