Next unresolved discussion button takes user to the right place

What does this MR do?

This MR fixes "next unresolved discussion button" failing to switch tabs when we' re on diffs tab and no unresolved discussions remained on diffs

This is done by making discussion_navigation mixin aware of entire discussion entry instead of just id - so we could check if our discussion is a diff and properly switch tabs if required.

Screenshots

Demo

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Related issue: #35360 (closed)