Make autofill manager service to not clear inline suggestions when IME input finishes

* This, together with the change on the sample IME, gets rid of the
  flicker on the notification pull down/up case, as well as switch
  from username to password.
* This doesn't fix the flicker when coming back from the attribution
  dialog, yet. As in that case the framework sends an empty suggsetion
  upon dismissing the dialog. Will explore fix for that in a separate
  patch.

Test: atest android.autofillservice.cts.inline
Bug: 157515522

Change-Id: Ia6d5d2b517cf400980fb602094c1abafb7100786