Similar to T76269: Merge projects javascript and MediaWiki-JavaScript

The MediaWiki-Documentation isn't used much and isn't really in itself an area of code that requires maintenance or has shared infrastructure that needs maintenance (aside from jsduck/Doxygen config maybe?)

Any thoughts on merging this into the generic tag Documentation, which seems to be what we've been using instead. There are 0 tasks in MediaWiki-Documentation not in Documentation.