Disable toggle on managed device with "Disallow add user" or "Disallow switch user"

Bug: 244279615
Test: croot && make RunSettingsRoboTests -j40 ROBOTEST_FILTER="com.android.settings.users.MultiUserSwitchBarControllerTest"
Change-Id: I3e89c8fac1828b4c9bb1c7df08687684981bda11
3 files changed