Also created a new MmsManager and moved imms APIs there. Will
make MmsManager @SystemApi in a later CL.
Test: basic sanity
Bug: 140763963
Merged-in: If22a85887c1aae0ab80562d58bc08c6965fd470f
Change-Id: If22a85887c1aae0ab80562d58bc08c6965fd470f
(cherry picked from commit 24c01a2f79)