Have IMMS report IME UID to AudioService

This is a follow up CL to our previous CL [1], which enabled
AudioService to be notified about the UID of the currently used IME.

Although there is no change in the overall approach, with the help
from InputMethodManagerService AuditoService can be notified new IME
UIDs more quickly especially when IMEs are switching to other ones
(e.g. due to user switching or profile switching).

 [1]: I11e17b13513627c88ccb8e4db66c5359e9ee7f7b
      ed4e8c3f

Bug: 147037345
Test: use voice input with Gboard 9.5.0 during a simulated RTT call.
Change-Id: I44e3331a7bad6d36227f7e2d0523dd14d933b6a1