GH-115060: Speed up `pathlib.Path.glob()` by not scanning literal parts (#117732)

Don't bother calling `os.scandir()` to scan for literal pattern segments,
like `foo` in `foo/*.py`. Instead, append the segment(s) as-is and call
through to the next selector with `exists=False`, which signals that the
path might not exist. Subsequent selectors will call `os.scandir()` or
`os.lstat()` to filter out missing paths as needed.