Make API documentation links language aware

Make API documentation links language aware

Links generated by the API are now aware of the user's preferred
language and will show documents in that language if available.

To test, log in to mediawiki.org and set your language preference to 'es',
then on an MediaWiki installation with this patch view the generated
expanded API help at `api.php?action=help&recursivesubmodules=1&modules=main`.
Each link to documentation on mediawiki.org should take you to its
translated /es subpage, if one exists.

Bug: T104518
Change-Id: I339a1f3ae1bce9d759cf251899d57c32b1def91e