Add `pathlib.Path.info` attribute, which stores an object implementing the `pathlib.types.PathInfo` protocol (also new). The object supports querying the file type and internally caching `os.stat()` results. Path objects generated by `Path.iterdir()` are initialised with status information from `os.DirEntry` objects, which is gleaned from scanning the parent directory.
The `PathInfo` protocol has four methods: `exists()`, `is_dir()`, `is_file()` and `is_symlink()`.
