Move #mHardwareKeyboardShortcutController to UserData

With this CL

 InputMethodManagerService#mHardwareKeyboardShortcutController

to UserData so that each user can keep maintaining its own instance.

The observable behavior should remain to be the same for single user
mode. For experimental concurrent multi-user mode, the controller is
now properly initialized in

  IMMS#experimentalInitializeVisibleBackgroundUserLocked().

Bug: 305849394
Test: presubmit
Flag: android.view.inputmethod.concurrent_input_methods
Change-Id: Ieb30952d33a6c74b7b6bd30baffb57ff4242accd