Enable Name and Avatar change without turning on multi-user

Primary user will be displayed in user list even when the
multi-user settings is disabled.
This will allow users to change the name and avatar of
primary user without enabling the multi-user feature.

Test: croot && make RunSettingsRoboTests -j40
ROBOTEST_FILTER="com.android.settings.users.UserSettingsTest"

Bug: 246732754
Change-Id: I4eb5aaf97630135960410bea7cdddc52b5848a1e