feat: make it easier to add content after the first post

[DavideIadeluca]

2.x port of #4050

Progresses #4060

Changes proposed in this pull request:

Reviewers should focus on:

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

Required changes:

• Related documentation PR: (Remove if irrelevant)

[SychO9]

is the intent after the first post of the discussion, or after the first of the visible posts? because i === 0 will always be the first of the currently visible posts, not necessarily the first post of the discussion.

For example, if you are viewing posts 200 - 220 of a discussion, the 200th is the first (i === 0)

[DavideIadeluca]

Yes that was most certainly the intention. Pushed a change which works much better now

[DavideIadeluca]

@SychO9 seems like phpstan/phpstan v1.12.18 (released yesterday) has broken CI here. Might you be able to look into this? Don't think it's a GitHub quirk this time around

[SychO9]

Thanks!

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Don't worry about the phpstan failure, will look into that separately.