Cycle unresolved threads

What does this MR do?

Related to: #16798 (closed)

• Change "Jump to first unresolved thread" button to "Jump to next unresolved thread"
• Update behavior to cycle through all unresolved threads instead of just jumping to the first one
• Remove the "jump to next thread" button from discussions

Screenshots

Old "jump" button

New "jump" button

Cycling discussions in action

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides

Availability and Testing