Automatically open resolved comments in merged PRs #1730

Hiding comments and resolving reviews is useful while finalizing PRs, but once the PR is done, all the discussion is hidden (I used this extensively while working on https://github.com/sindresorhus/refined-github/pull/1694 to keep track of all the requests)

#1729 could do this with a click, but an automatic feature could work automatically even on collapsed comments (via onNewComments)