Move mCurTokenDisplayId from IMMS to InputMethodBindingController

With this commit mCurTokenDisplayId starts belonging to
InputMethodBindingController rather than InputMethodManagerService.

While this is not a mechanical change, that there is supposed to be no
observable behavior change.

Bug: 305849394
Fix: 341179600
Test: presubmit
Change-Id: If9cdc8ee7c9c0726e9712d0a36cf2e9b05b4099e