Call StatusBarManagerInternal methods only for the current IME user

With recent CLs we now started triggering methods like

 * InputMethodManagerService#hideStatusBarIconLocked()
 * InputMethodManagerService#updateSystemUiLocked()
 * InputMethodManagerService#updateStatusIcon()

not only for the current IME user but also for any running background
user. These methods eventually trigger the following three methods.

 * StatusBarManagerInternal#setIcon
 * StatusBarManagerInternal#setIconVisibility
 * StatusBarManagerInternal#setImeWindowStatus

At least on phones and tablets apparently they are not ready to be
used by multiple users on multiple displays at the same time. To
minimize the risk of confusing existing SysUI implementations, let's
call the above methods only for the current IME user unless

  InputMethodManagerService#mConcurrentMultiUserModeEnabled

is set to true.

For concurrent multi-user mode, the corresponding SysUI is responsible
for making sure that it would not be messed up.

Bug: 357178609
Test: presubmit
Flag: android.view.inputmethod.concurrent_input_methods
Change-Id: I5918e074a833a2dd6bc3e2555995b6461931b438