Fix deletes not reaching every server that interacted with status

[Gargron]

Extract logic for determining ActivityPub inboxes to send deletes to to its own class and explicitly include the person the status
replied to (even if not mentioned), people who favourited it, and people who replied to it (though that one is still not recursive)

[ClearlyClaire]

I'm ok with the general idea, and factoring it out looks cleaner and is easier to reason about. As for the failing test, I have to admit I have no clue what's going on, for some reason I don't understand, @status.reblogs is empty even though a reblog has been instantiated.

It should also be noted that instances that fetched the toot in any way without actually interacting with it won't necessarily get a delete, and it mostly relies on intermediary instances forwarding the Delete. But it should be an improvement over the status quo nonetheless.

[Gargron]

The unit test caught a real issue. Reblogs were removed before StatusReachFinder was called, this was fine before because reblogs were preloaded into an instance variable. But I see no reason why the order of execution should be that way anymore, so I changed it. Also, since the preloads were no longer used more than once in the class, I replaced them with potentially more efficient find_each calls.

[Gargron]

I also identified some inefficies. When removing a reblog, the class would make queries for the reblog's mentions, media attachments, tags, etc. Since reblogs don't possess those, we can cut down on those queries. Also, due to using pluck on the tags, the tags actually got queried twice, once the IDs for featured tags, and then the names for the timelines.

[ClearlyClaire]

Good catch with the reblogs stuff. This seems better overall, but there's one thing I'm not sure about (though it shouldn't be a big issue), see inline comments.

[ClearlyClaire]

I understand this is to avoid fetching account information from the database, but this will send events about remote accounts to redis. Is it worth it? Does it make sense?

[Gargron]

You’re right... but publishing to a channel with no subscribers should be O(0) so probably fine this way.