imms: reset window status on disconnect

- IMMS does not call setDismissImeOnBackKeyPressed when service
  disconnects (e.g. in case of InputMethod app update).
- Call setDismissImeOnBackKeyPressed to
  reset the state on service disconnect.

Test: Start input method and run `adb shell am crash com.google.android.inputmethod.latin` a few times until the ANR
dialog shows up. Verify power button press still works.

Bug: 233076484
Change-Id: I212347d67b58446e060e8492a7a095e0e16449ea