Adds a method to check whether a foreground user has permission to switch
to other users.

Additionally, checks for DISALLOW_USER_RESTRICTION before invoking switch in
CarUserManagerHelper methods. We cannot remove a user if we can't switch out of
that user.

Change-Id: I359213b5d9e92ec726a7fe4c03701098708c3ec0
Fixes: 112090084
Test: atest CarUserManagerHelperTest
2 files changed