Introduce Emergency number functions APIs

- getCurrentEmergencyNumberList
- getCurrentEmergencyNumberList (per categories)
- isCurrentEmergencyNumber

Note: the implementaion from PhoneInterfaceManager is empty, but the names
of the APIs need to be finalized so that the usages and test plan are not
blocked.

Bug: 112657134
Test: Treehugger
Change-Id: I854db34f4378f35f99c3d8133bf35f3d0b3aad2b