Exports a group of drawing elements as a PDF file (see example). In the exported file, the group is positioned at
[0, 0]. Its dimensions are used as the default dimensions for the image.
Scene images have to be of same origin or CORS-enabled.
The export operation is asynchronous and returns a promise.
The Group to export.
The PDF Export options.
Promise<string> - A promise that will be resolved with a PDF file encoded as a Data URI.