Hovering over `Closed` label should show who and when it was closed

Description

With long threads, sometimes which continue on past an issue is closed, it is helpful to be able to quickly figure out when an issue was closed, who did it, and why (if it was because of merge or not). I suggest adding this information as hover text on the Closed indicator at the top of the issue.

Proposal

Links / references

Documentation blurb

Overview

What is it? Why should someone use this feature? What is the underlying (business) problem? How do you use this feature?

Use cases

Who is this for? Provide one or more use cases.

Feature checklist

Make sure these are completed before closing the issue, with a link to the relevant commit.