This was definitely added at someone's request, since I wouldn't have
put it here. But it's displayed below in the details section already and
also not displayed in the updated "wedge" in the new design.
See https://github.com/ppy/osu/discussions/17537 for discussion.
We've seen multiple cases where DrawableHitObject are stuck in the lifetime management container
due to not implementing a judgement (meaning they are never "hit" or "missed"). To avoid this going forward
CreateJudgement() must be implemented and return a non-null judgement.
This fixes BananaShower and JuiceStreams in osu!catch.
This also makes HitObject abstract and cleans up convert HitObject implementations.