rust-hgpath: add HgPath and HgPathBuf structs to encapsulate handling of paths
This change is a direct consequence of this discussion on the mailing list:
https://www.mercurial-scm.org/pipermail/mercurial-devel/2019-August/133574.html
The implementations of `HgPath` and `HgPathBuf` are, for the most part, taken
directly from `OsStr` and `OsString` respectively from the standard library.
What this change does *not* yet do is implement the Windows MBCS to WTF8
conversion, but it lays the basis for a very flexible interface for paths.
Differential Revision: https://phab.mercurial-scm.org/D6773
{
"conduit_uri": "https://phab.mercurial-scm.org/api",
"repository.callsign": "HG",
"arc.land.onto.default": "@",
"base": "hg:.^"
}