Dereference prev + next posts in public threads

[tsmethurst]

Right now threads often appear incomplete because GtS doesn't fetch any of the previous or next posts in a thread, so users see only fragments of conversations.

To offer a more complete view, we should dereference the whole chain of posts that a given post replies to or is replied to by. But we should only do this for posts that are Public (or possibly Unlisted), and not followers-only posts.

This dereferencing could be done here for example:

gotosocial/internal/federation/dereference.go

Line 194 in 0386a28

func (f *federator) DereferenceStatusFields(status *gtsmodel.Status, requestingUsername string) error {

To figure out where replies etc are, we can use the replies field on status activity representations:

  "replies": {
    "id": "https://example.org/users/some_user/statuses/106691726504418392/replies",
    "type": "Collection",
    "first": {
      "type": "CollectionPage",
      "next": "https://example.org/users/some_user/106691726504418392/replies?only_other_accounts=true&page=true",
      "partOf": "https://example.org/users/some_user/106691726504418392/replies",
      "items": []
    }

and the inReplyTo field:

 "inReplyTo": "https://example.org/users/a_different_user/statuses/106691640442578059"

[tsmethurst]

Implemented with #132