s3: smbd: Correctly canonicalize any incoming shadow copy path.

s3: smbd: Correctly canonicalize any incoming shadow copy path.

Converts to:

@GMT-token/path/last_component

from all incoming path types. Allows shadow_copy modules
to work when current directory is changed after removing
last component.

Ultimately when the VFS ABI is changed to add a timestamp
to struct smb_filename, this is where the parsing will be
done.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12531

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Uri Simchoni <uri@samba.org>