Update user related fields when InputMethodSettings#switchCurrentUser

Ensure mUserAwareContext/mResolver/mRes in InputMetodSettings may
out-of-sync after switchCurrentUser that some utilility methods depends
on this will get wrong result, like
- getEnabledInputMethodSubtypeListLocked (Depends on the locale
  of the user resources configuration)
- isShowImeWithHardKeyboardEnabled (Depends on the content provider of
  the user to query settings)

Also, added a unit test to verify this behavior works as expected.

Bug: 251814906
Test: atest InputMethodUtilTest#\
       testInputMethodSettings_SwitchCurrentUser
Change-Id: I6d514310623d74972e1f9b8a32bb201a635c601b