`pr-easy-toggle-files` improvements #3793

Three suggestions for the pr-easy-toggle-files feature:

1. Enable <kbd>alt</kbd>-clicking to toggle all files. This already works when clicking directly on the arrow, but not on the whole file header bar. Test URL: Any PR's files tab.
2. Enable the feature on Unchanged files with check annotations that are shown in the files tab below the files that actually changed. Test URL: https://github.com/OpenLightingProject/open-fixture-library/pull/1619/files?file-filters%5B%5D=
3. Enable the feature in compare view. Test URL: https://github.com/typicode/husky/compare/v4.3.0...v4.3.5