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.

#require rustfmt test-repo

  $ . "$TESTDIR/helpers-testrepo.sh"

  $ cd "$TESTDIR"/..

Warning: Keep this in sync with hghave.py
  $ RUSTFMT=$(rustup which --toolchain nightly-2021-11-02 rustfmt)
  $ for f in `testrepohg files 'glob:**/*.rs'` ; do
  >   $RUSTFMT --check --edition=2018 --unstable-features --color=never $f
  > done