Extend no-whitespace button (from `faster-pr-diff-options`?) to "Comparing Changes" page #3870

<!-- 1. Make sure your requested feature makes sense for Refined GitHub: https://github.com/sindresorhus/refined-github/issues/2960 2. Include a full URL where the feature should appear. -->

?w=1 is a valid flag for https://github.com/drichard/mindmaps/compare/master...eitwizlearn:master pages; hence it could make sense to add the "No Whitespace" button in those pages