Add ability to collapse entire comments #4808

Description

• In the top-right of a comment, add a chevron icon that lets you collapse a comment to just the title bar.
• Preserver collapsed issue comments between pageloads

This is useful in issues where you need to reference only specific issues and are scrolling past intermediary ones.

This is not Hide Comment, which is used to hide comments from everyone. This is a convenience behavior.

I searched around and did not see that this exists yet, and I'm not seeing it somehow. If so, please point me at it.

Screenshot

<img width="333" alt="image" src="https://user-images.githubusercontent.com/1409710/134466106-2866e958-854f-4ef4-93f7-dafc9e05df30.png">

I'd probably put this in the far right, despite the ellipsis begging to be the last item of a list.

Reason is, window management typically puts this minimize type behavior in the corner. Also I don't think its good jam something to the left of where the comment author is located.

Example URL

https://github.com/PostHog/posthog.com/issues/2018