Add a documentation in EmergencyNumber#getNumber
If the number starts with a carrier prefix, the
carrier prefix is configured in
{@link CarrierConfigManager#KEY_EMERGENCY_NUMBER_PREFIX_STRING_ARRAY}.
This is important because it provides a solid reference for Apps to
strip the prefix, which they may not prefer to display.
Bug:
137225076
Test: Treehugger
Change-Id: I1f6bd74f1d6eb86fe3326246e0ddb08b9cf7ac11
Merged-In: I1f6bd74f1d6eb86fe3326246e0ddb08b9cf7ac11
(cherry picked from commit
552a58ae51e4f8ef1a0bcefe9a475b4511454c17)