Resolve ""Jump to first/next unresolved discussion" jumps to resolved discussions"

What does this MR do?

It solves the broken navigation buttons to jump to first unresolved discussion and also jump to next unresolved discussion.

Also no longer displays link to "next unresolved discussion" on the last discussion on the page (depending on which view you're in).

Are there points in the code the reviewer needs to double check?

Keen on checking if this doesn't worsen memory footprint that much for REALLY large MRs, with hundreds of discussions.

Why was this MR needed?

It was broken.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a Frontend maintainer
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them

What are the relevant issue numbers?

Closes #48817 (closed)

Closes #48602 (closed)