Feature summary (what you would like to be able to do and where):
Add 'view diff' & 'edit the latest revision' links to MediaWiki:editingold.
Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
Used when editing an out-of-date revision of a page (https://www.mediawiki.org/w/index.php?title=Extension_talk:Page_Forms&action=edit&oldid=5974044 for example, or https://www.mediawiki.org/w/index.php?title=Extension_talk:Page_Forms&veaction=edit&oldid=5974044 with VisualEditor enabled).
Benefits (why should this be implemented?):
Editors can see diff between the out-of-date revision and the latest version and jump to the latest version conveniently (though there're already links in revision-nav, they are unclickable in VisualEditor).
Before:
After: