rust-filepatterns: add `rust-cpython` bindings for `filepatterns`
This change adds the `rust-cpython` interface for top-level functions and
exceptions in the filepatterns module.
Contrary to the Python implementation, this tries to have finer-grained
exceptions to allow for better readability and flow control down the line.
Differential Revision: https://phab.mercurial-scm.org/D6272
(binary:application/octet-stream)