Add IO::Path.user/group methods
Add IO::Path.user/group methods

- .user returns the uid of the path, or a failure if it doesn't exist
- .group returns the gid of the path, or a failure if it doesn't exist

This basically exposes the nqp::const::STAT_UID and nqp::const::STAT_GID
slots of nqp::stat.

I did consider making these allomorphs with the user / group name in string
format as well, but that turned out to be pretty difficult to do without
NativeCall or calling some external program to get the group name.

I also have no idea what these nqp::stat slots mean on Windows.

Lack of this functionality mentioned in some private email conversations
with a sysadmin wanting to use Raku more.

tony-o/rakudo,rakudo/rakudo,tony-o/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,labster/rakudo,tbrowder/rakudo,rakudo/rakudo,salortiz/rakudo,tbrowder/rakudo,rakudo/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,salortiz/rakudo,tony-o/rakudo,salortiz/rakudo,salortiz/rakudo,labster/rakudo,tbrowder/rakudo,salortiz/rakudo,MasterDuke17/rakudo,labster/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo,labster/rakudo,labster/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,tony-o/rakudo,tbrowder/rakudo,tony-o/rakudo,rakudo/rakudo,rakudo/rakudo,rakudo/rakudo,salortiz/rakudo