statecheck: added support for cmdutil.afterresolvedstates
This removes `afterresolvedstates` from `cmdutil` and adds
support for it in `_statecheck` class.
A new flag `continueflag` is added to the class to check whether an
operation supports `--continue` option or not.
Tests remain unchanged.
Differential Revision: https://phab.mercurial-scm.org/D6551
#require docutils gettext
$ $TESTDIR/check-gendoc sv
checking for parse errors