🐛 fix search state bug & missing last result

[cathysarisky]

closes #21343

This fixes an issue in sodo-search where early results (for example, matching the first letter typed in the search box) would get "stuck" in the display, due to failure to update state (or actually, lacking state).

Converted PostItems to a component, and gave paginatedPosts state.

I also fixed an undocumented bug where the last search result didn't appear, due to an error in with slice's register.

[kevinansfield]

@cathysarisky the use of state and useEffect added here is a React anti-pattern. Preferred approach is to use posts to build paginatedPosts directly in the first render rather than going the round-about way of using an effect to update state and causing a second render 🙂

If building the list directly in the first render is causing problems then we have a different issue somewhere that needs addressing.

[kevinansfield]

Ugh, sorry, I'd missed how we're using maxPosts state here and how posts changing resets the number of posts shown - this is the problem with useEffect for things like this, it makes the flow much harder to follow!

Seems like there's a refactor waiting here somewhere but your fix looks good for now 🙏