KR UI redesign session 6: Activity & Comments (spans Create, Plan, and Secure)

From &7151 (comment 735055147):

What are some challenges you're facing with the current design?

• Since comments can be threaded, comments don't always appear in chronological order, making it difficult to find certain things (namely- "what happened since I last looked at this?")
• On merge requests, comments can be on either the Overview tab or Changes tab. Diff comments appear in both places. Outdated diff comments appear only on the Overview
• All activity items are given equal weight, despite some being more important than others. For example, @user merged this is more important than @user mentioned this in a comment

What are some key areas you'd like addressed?

• Update different types of activity to call attention/decrease visibility depending on activity type
• Maybe combine certain activity types if the same type is listed multiple times
• brainstorm ideas to help users understand what happened since they last visited (this might be a bit too big for this OKR 🤔)

How could this benefit other areas of the product?

This focuses mostly on Code Review and Plan (issues & epics) but also touches areas like Secure (activity on a reported vulnerability)

Links or screenshots.

Slide deck from last UX showcase (Slides 8-11 highlight this problem in Code Review)