ItemList API improvements

[askvortsov1]

Feature Request

Is your feature request related to a problem? Please describe. ItemList currently serves as an ordered associative structure, with order determined by integer "positions". It would be convenient and more self-documenting if items could be inserted relative to other items. For instance:

• items.after('delete').add('something', hello)
• items.before('delete').add('something', hello)
• items.after('delete', 10).add() // specify a fallback priority
• items.after(['foo', 'bar'], 10).add() // specify multiple items to add after

Initially proposed in https://github.com/flarum/core/issues/1317

Describe the solution you'd like We'd need to include a modified topological sort (like https://github.com/flarum/core/pull/2317), that also includes support for integer-based priority.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. We do this to keep the amount of open issues to a manageable minimum. In any case, thanks for taking an interest in this software and contributing by opening the issue in the first place!