Resolve IME userId from display/window for multi-user IME

With this CL we start resolving IME userId from displayId or window
token on concurrent multi-user mode by using

  UserManagerInternal.getUserAssignedToDisplay().

There must be no behavior change in single-user mode.

Bug: 350386877
Test: manually verified
Flag: android.view.inputmethod.concurrent_input_methods
Change-Id: I31f9f1566c52f0dc5b8f730cc2c59a59aa3fcd6b