Guests can config wifi, but not shared wifi

With the new usage of "shared wifi" vs. "private wifi", we wish to allow
Guests to use the latter but not the former. So we update their
restrictions accordingly, both for new and pre-existing guests.

Moreover, since the headless system user will now also make use of the
shared vs. private distinction, we make system user restrictions
customizable via the standard mechanism. That is, we deprecate
config_defaultFirstUserRestrictions (which now, for convenience,
continues to exist but only as an overwritable default), and instead
rely on config_user_types.xml (as we do for all other user types).

Moves the instantiation of LocalService to be earlier otherwise we can
call it before it has been initialized, crashing the system. This was
already possible before, but probably didn't come up in practice.

Test: manual
Flag: android.multiuser.user_restriction_config_wifi_shared_private
Bug: 390240471
Bug: 428282717
Change-Id: I1a6f4f4a16fe062c0659d9b2ed326d7b2f72eaa0