advancementOrigin flag

@arbron I spotted a flag advancementOrigin on items granted by advancements but don't see it used anywhere atm.

Is there a use-case you have in mind for this flag?

I'm interested in organizing features on a character sheet under the class/subclass that granted them atm and I have a feeling this will let me do that, but don't really want to rely on that if it's unstable.
It’s not used at the moment, but that seems like a great way to make use of it. There isn’t any reason it should change in the future