Hook up userId in IMMS#showInputMethodPicker()

With this CL, a valid userId starts being propagated into
showInputMethodPicker() implementation when the concurrent multi-user
IME is enabled. While InputMethodMenuControllerNew cannot be used from
multiple users at the same time, propagating the right user ID should
still make sense.

There must be no observable behavior change in the single user mode.

Bug: 349904272
Test: presubmit
Flag: android.view.inputmethod.concurrent_input_methods
Change-Id: I0963968ad2a94144178d72f3d28ee8d31ac4f46e