Add more AbuseFilter vars

AbuseFilter::getEditVars adds a couple of new vars (e.g. added_lines), which are
based on new_wikitext and old_wikitext.
We already supply new_wikitext & old_wikitext with Flow data, so we might as
well make these additional operators available to Flow filters.

Change-Id: Ia54586f99e667d40b727fdde3096081ea5de6c85
Merge "Add more AbuseFilter vars"