Special:PagesWithProp: Distinguish content from interface

Distinguish information about property values being hidden from the
actual values visually by making it italicised.

Added a new module, mediawiki.special.pagesWithProp.

Followup to Ib2db241a.

Bug: 51888
Change-Id: I6a0246e9b2a97b59503395ece7f80442ae3e0c69
Merge "Special:PagesWithProp: Distinguish content from interface"