Shortcut Helper - Fix it not showing on a secondary user

- The activity needs "showForAllUsers" to be true, for it to show
- The broadcast needs to be registered for all users, since the Activity
  sends broadcast using their own user id

Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Test: Manual
Fixes: 343884480
Change-Id: I0b9ca11c42d709c06516f2f4a1492d0e071bd016