Shortcut Helper - Set System as default category when launcher is open

+ Makes sure the helper works on HSUM builds by using the current user
  id in calls to PackageManager and RoleManager

Flag: com.android.systemui.keyboard_shortcut_helper_rewrite
Test: Unit tests in this CL
Test: Manually - Open the helper while on Launcher and when on Chrome. The "Current app" category is only selected while not on Launcher.
Test: Flash a HSUM build and make sure everything works
Fixes: 355160597
Fixes: 354879386
Fixes: 354879255
Change-Id: Icc664238e744157e2604e5e27e6f9dfcb4aded2c