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
# See http://EditorConfig.org for the specification
root = true
[*.py]
indent_size = 4
indent_style = space
trim_trailing_whitespace = true
[*.{c,h}]
indent_size = 8
indent_style = tab
trim_trailing_whitespace = true
[*.t]
indent_size = 2
indent_style = space
trim_trailing_whitespace = false