UserProperties is @SystemApi & migrate 2 old props

We don't need UserProperties to be public right now, so making it
SystemApi instead.

We also migrate two old properties from UserManager to UserProperties.
They were created before UserProperties existed, but are naturally
properties and belong in the UserProperties class.
These properties are SystemApi.

Bug: 237399048
Test: atest android.multiuser.cts.UserManagerTest
Test: atest com.android.server.pm.UserManagerTest
Test: atest UserManagerServiceUserTypeTest
Test: atest UserManagerServiceUserPropertiesTest

Change-Id: I63bef28ab3cf96de8ba710ae68dbe8f4847d3b5c