Restore `reactions-avatars`

Github no longer loads who reacted in the aria-label until you hover 😞

_Originally posted by @yakov116 in https://github.com/sindresorhus/refined-github/issues/3120#issuecomment-632331245_

reactions-avatars stopped working (https://github.com/sindresorhus/refined-github/issues/3120) because of this change.

The feature used to look like this:

Since the usernames are no longer available on the DOM until it’s too late, the only fix is to load these usernames via the API.

The problem is that this call might be rather large on very active discussions, so this might no longer be worth it.

PR welcome to figure out what changes are required and what the impact would be on large conversations like https://github.com/facebook/react/issues/13991

[yakov116]

Looks like github went back to the old way!!

[fregante]

Neither solution is great, I’d very much prefer triggering GitHub’s own queries on hover than calling the API, as I mentioned in my comment.

This would require minimal changes to the current code:

+ trigger mouseenter
+ wait for attribute change
  read aria-label attribute
  etc