hg-core: vendor Facebook's path utils module The added file was imported from https://github.com/facebookexperimental/eden/blob/d1d8fb939a39aa331ae7f162c39cbcaa511d474b/eden/scm/lib/util/src/path.rs without modifications. The file is not yet integrated into our project. This will be done in subsequent commits. Differential Revision: https://phab.mercurial-scm.org/D7573