Fixes bug where users could add other users when they should not have had that ability.

Consolidates logic in canCreateUser and canCreateGuest in a new method canAddMoreUsers that also checks UserManager.canAddUsers with specified  user type

Removes the check anyoneCanCreateUsers, since currentUserCanCreateUsers is a sufficient check. currentUserCanCreateUsers checks that both the current user and the system user do not have the DISALLOW_ADD_USER restriction.

Removes unnecessary isAddUsersFromLockScreenEnabled check in canManageUsers logic.

Uses (isDeviceLocked or isAddUsersFromLockScreenEnabled) condition rather than isAddUsersFromLockScreenEnabled

Flag: NONE
Fixes: 270370602
Test: UserSwitcherInteractorTest.kt, local hsum and non hsum testing
Bug:270370602

Change-Id: I85de669c9daee7b06825601f74b5193df0f31e5b