Fix IME icon flicker when switching apps

- Add disableImeIcon parameter in IMMSInternal#updateImeWindowStatus
  to disable back icon & IME switch icon in navigation bar
  for RecentsAnimatinController when task switching happens.

- Fix IME icon flickering when invoking hideInputMethodMenuLocked during
  unbind current client, ensure updating IME icon only when the IME
  picker dialog exists.

Fix: 189282303
Test: manual as below steps:
     1) Launch an app with shown IME
     2) Swipe out the app to the launcher, make sure IME icon didn't
        flicker when going to launcher.
     3) Launch step 1) app again, swipe-up to recents, make sure IME
        icon didn't flicker when going to recents
     4) Launch step 1) app again, swipe left or right to the next app
        task without showing IME.
     5) Make sure IME icon didn't flicker when going to the next app.
Change-Id: Ib55db60c29abf5b389ad60bfa56e5e8fb2c75f1f