rust-filepatterns: match exact `rootglob`s with a `HashSet`, not in the regex This optimization yields some very interesting results in `rootglob`-heavy repositories. I build a test repository of the following structure: ``` root /<uuid>/build/empty_file ... repeat for 4000 entries ``` and a `.hgignore` containing the corresponding 4000 `rootglob` entries pointing to all `build/` folders. Rust+c `hg status` goes from 350ms down to 110ms. Differential Revision: https://phab.mercurial-scm.org/D8491