The `keystroke` function in `common_utils.js` was added in gitlab-ce!28914. We already ship with a library, [Mousetrap](https://craig.is/killing/mice), that handles keyboard shortcuts, but it is outdated and doesn't support capturing keyboard events over a single element, like a textarea. Working around this limitation would have been messy, so `keystroke()` was introduced instead. gitlab-ce#63182 proposes upgrading Mousetrap to the latest version. Then, we should remove `keystroke()` and make the markdown editor use Mousetrap to capture keyboard shortcuts instead.