When the existing search results don't contain an exact match
(see previous patch), perform an additional search for the
title. This uses OpenSearch. This is recommended in multiple
places and also used in the quick search field at the top of
MediaWiki.
Again, I came to the conclusion that an isolated unit test
would be complicated and not test much anyway. Better test
on-wiki.
Bug: T274903
Change-Id: Ib575248e089ff66814400202d224deff6369c772
