Improve handling of suspended accounts

[ClearlyClaire]

Currently, suspending an user means deleting pretty much any information related to them, but ongoing work (#14726 and related Pull Requests) attempts to make account suspension reversible (in order to be able to revert erroneous suspensions, but this could also be used for temporary suspensions).

Since #14765, users marked as suspended do not appear in following/followers lists, even if they are still technically following an user. This makes total sense if the suspension happens to be final.

However, consider the following situation: Bob follows Alice, gets suspended, then later gets unsuspended. This means that while Bob is suspended, he won't appear as a follower to Alice, but at the moment he gets unsuspended, he will show up again. This can be surprising behavior, especially if the time between the suspension and the cancellation of such suspension is long.

Worse, should Alice make sure Bob cannot read her private toots, she cannot do that until Bob gets unsuspended. In the time window between Bob being unsuspended and Alice noticing Bob is still following her, Bob can read her private toots, including those posted during Bob's suspension (assuming Bob is on Alice's server or the server of another of her followers).

Proposal

Therefore, I think it makes more sense to:

• have the following relationships be automatically severed at the time of the suspension
• when the suspension gets cancelled, send a follow request for each of the former following relationships

Concerns

• receiving a follow request from someone you thought was already following you (because you missed the fact they were suspended) might be surprising and confusing
• if the suspended account is following a lot of people, cancelling the suspension might cause significant load
• federation-wise, care should be given to not ignore the new follow requests (e.g., incorrectly believing the account to still be suspended)