Per T328947:

We want to remove the parentheses from the html markup for revision tools so that we can present them in widgets where those separators aren't desirable
https://gerrit.wikimedia.org/r/plugins/gitiles/mediawiki/core/+/refs/heads/master/includes/diff/DifferenceEngine.php#860

We can replace them with css-based separators using helpers
https://github.com/wikimedia/mediawiki/blob/master/resources/src/mediawiki.interface.helpers.styles.less#L65-L78

We should get setup with pixel to ensure that our changes don't impact desktop
https://github.com/wikimedia/pixel