Control user switching UI visibility according to config

Bug: 375394047
Test: atest UserDetailsSettingsTest UserSettingsTest
Test: build platform with config overrides, check the result
Flag: EXEMPT Desktop-only change
Change-Id: Iaf1ac6c98a648066bf77b069039dcd59e243835f

src/com/android/settings/users/UserSettings.java

@@ -287,7 +287,7 @@ public class UserSettings extends SettingsPreferenceFragment
         final SettingsActivity activity = (SettingsActivity) getActivity();
         final SettingsMainSwitchBar switchBar = activity.getSwitchBar();
         switchBar.setTitle(getContext().getString(R.string.multiple_users_main_switch_title));
-        if (!mUserCaps.mIsGuest) {
+        if (!mUserCaps.mIsGuest && mUserCaps.mUserSwitchingUiEnabled) {
             switchBar.show();
         } else {
             switchBar.hide();