Otherwise, the behaviour can lead to unexpected results, resulting
in removing an entire tree that's not necessarily under the root.
Furthermore, this change is needed if are to properly handle dir
symlinks on Windows. Without explicitly requiring that a directory
or file is opened with `FILE_OPEN_REPARSE_POINT`, Windows automatically
dereferences all symlinks along the way. This commit adds another
option to `OpenDirOptions`, namely `.no_follow`, which defaults to
`false` and can be used to specifically open a directory symlink on
Windows or call `openat` with `O_NOFOLLOW` flag in POSIX.
e0b77a6b77