Introduce IMMS#getInputMethodBindingController()

This is a mechcanical refactoring CL that aims to simplify the code by
taking advantage of per-user InputMethodBindingController instance we
recently introduced [1].

As you can see in this CL, the following code snippet can be seen so
many places.

 final var userData = mUserDataRepository.getOrCreate(mCurrentUserId);
 final var bindingController = userData.mBindingController;

Let's simplify them by introducing

 InputMethodManagerService#getInputMethodBindingController(userId).

There must be no observable behavior change.

 [1]: Id6e9eca6caaa8edde8c4a405448c31c0ca986509
      2238ecd4

Bug: 325515685
Bug: 339358344
Test: presubmit
Change-Id: I3e2d196e91c9adbc326388a6ebbbbcfe6b46b196