Add "IPTC:PersonInImage" metadata field to the files

When doing face recognition and saving the face region to the XMP files, please also add the IPTC field “PersonInImage”.
It is simply the list of all persons, that are tagged on that image and is a standard way, read by many application.
It is especially useful for application, which don’t read the region information, but can read this field to refer to people depicted on the photo.