Gets the data object that was passed to a lightbox.
Retrieves the data object, if any, that was passed when a lightbox
was opened with the openLightbox() method.
If a lightbox was opened in any other way, getContext() returns undefined.
To pass data to a lightbox, it must be opened programmatically using the openLightbox()
method. Lightboxes that are opened automatically on page load, or with a link from a page element don't receive passed data.
Note: While the editor and dashboard now refer to these elements as popups, the API methods and documentation continue to use the term lightbox for consistency and backward compatibility.