Adding @throws tags for EmergencyNumber APIs so that callers are aware
that they can throw.
Test: Build; docs only change.
Bug: 134100020
Fixes: 152231444
Merged-In: Ic6bcd32ab93a97a8d075e720acb5fc17612a3984
Change-Id: Ic6bcd32ab93a97a8d075e720acb5fc17612a3984
(cherry picked from commit 5fe27428f0)