The approach taken here is the same as in core for magnify links on
thumbs in Id46d1b2ab1af3baebff13e10f1485f3cfd9a4b37
The gist is that resource attributes are added on the mw-file-element so
that the necessary url is present in the html. A class is also added to
the wrapper element that designates where the link should be positioned.
Finally, a script adds the link which styles in appropriately.
Bug: T329364
Depends-On: Id46d1b2ab1af3baebff13e10f1485f3cfd9a4b37
Change-Id: I20130fd39135dfd5074590ee9c2b6e01693384e4
