Port the “unfold thread” feature from Mastodon's UI to glitch-soc flavour

[ClearlyClaire]

This is a very much in progress PR aiming to implement he “unfold thread” feature of Mastodon (fixes #387). Unfortunately, as the code has diverged quite a bit and is pretty hard to reason about, it will take some work.

• Port related changes to column headers
• Refactor the collapsed/extended logic to make it easier to reason about
• Port the feature itself

[ClearlyClaire]

Porting this feature really is a pain, in terms of user interface, because of collapsed toots. The crux of the problem is the following:

1. This change makes the folded/unfolded status for content warnings shared across every view of a toot
2. So far, the collapsed/not-collapsed state of a toot is specific to a view of a toot. It makes sense because one may want toots in their notifications column collapsed while not having them collapsed in their TL
3. It does not make much sense for a collapsed toot to have have its content warning unfolded, especially as that would cause the “fold/unfold” button to not have seemingly no effect on collapsed toots

In the current state of this PR, point 3 is ignored, and the “CW unfolded but collapsed view” state is possible, which is a regression.
I'm not too sure how to proceed, but I'm considering changing 1 to keep the previous behavior, but it will be more work and it will not bring Mastodon and glitch-soc codebases closer…

[marrus-sh]

Yeah I am not a fan of having CW folding status shared across every instance of the toot for a number of reasons:

1. In notifications it makes things really awful if you have a bunch of notifications on the same, CW'd toot, and then you expand it (all of the instances of the toot in the notifications bar expand, causing you to completely lose your place)
2. In general, I think rendering details should be kept out of redux (this is a personal stance which upstream does not share) and that the redux store should be reserved just for API stuff

I think upstream's approach to this was kinda hacky and not great from a useability perspective and results (imho) from an overreliance on Redux as a catch-all solution to every problem, which it isn't :P. Instead this should be handled via a passed prop/state from the conversation column (React idiomatic if a little complicated) or via Events (the better, cleaner solution, but not in line with any of the existing codebase).

[ClearlyClaire]

Alright, this is something I wasn't too sure about. I'll try to rework the PR to fold/unfold the toots in the thread view only, not using the Redux store for that.

[ClearlyClaire]

Updated to not use redux. The CW fold/unfold state is now specific to each view of the toot, unlike in tootsuite/mastodon. Tried to keep the differences with tootsuite/mastodon minimal nevertheless.

[hannahwhy]

@marrus-sh When you get a chance, can you look over these changes?