repoview: add an explicit set of all filter that show the wc parents

The `visible` set will always show the working copy parents. We record this in a
specific set. This will allow to fast path some access.

Differential Revision: https://phab.mercurial-scm.org/D7490

mercurial/repoview.py

@@ -177,6 +177,9 b' filtertable = {'
     b'base': computeimpactable,
 }
 
+# set of filter level that will include the working copy parent no matter what.
+filter_has_wc = {b'visible', b'visible-hidden'}
+
 _basefiltername = list(filtertable)