Update EmergencyNumber API docs to indicate they can throw.

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 5fe27428f06a7bfd439db96d0418323687010986)
1 file changed