ntfs: support following Windows native symlink with relative paths

ntfs: support following Windows native symlink with relative paths

Make ntfs_make_symlink() parse native Windows symbolic link reparse
payloads when the SYMLINK_FLAG_RELATIVE bit is set.
Implement the following changes:
 * Add a dedicated on-disk layout definition for symbolic link reparse
   data.
 * validate the UTF-16 name ranges before decoding them.
 * convert the substitute name into the mount's NLS and normalize path
   separators.

Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>