match: fix the rust-side bug in visit_children_set for rootfilesin matchers
The fix is checked by `test_pattern_matcher_visit_children_set` test,
which is what caught the bug in the first place, but also by an end-to-end
test that I made for this purpose.
Accept the new results of Cargo tests
Many of these were already annotated with "FIXME", which is a good sign.
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).