Mostly places that can interact with imported replays.
There are other places that use the online ID as a sort tiebreaker, or
to check presence of a score on results screens, but they should
probably still continue to only use `OnlineID`, since all scores with a
legacy online ID should have an online ID, but the converse is not
generally true.
Introduces some error at all times, but if we're to store scores everywhere as
`long`, then the same precision should be applied to the "during
gameplay" path as well.
