Show toasts from system/sysUI to all users

The package name test is safe:
* If it's used by Toast class in an app, apps have access to layout
  params anyway via getWindowParams() and applied flag is already
  protected by INTERNAL_SYSTEM_WINDOW permission.
* If it's used by ToastUI class in sys UI on behalf of another app,
  sys UI is trusted domain and can't be messed up by another app. It
  also has INTERNAL_SYSTEM_WINDOW permission.

Bug: 149408635
Test: atest ToastUITest android.widget.cts.ToastTest
      android.widget.cts29.ToastTest android.server.wm.ToastTest
Test: Change phone to vibration/silent in secondary user and observe
      toast is displayed.

Change-Id: I227e9f74166300fcb3ba8f3871b464afe6ec6a28