PdfAnnotationCallback typedef
        PdfAnnotationCallback =
     void Function(Annotation annotation)
    
    
Signature for SfPdfViewer.onAnnotationAdded, SfPdfViewer.onAnnotationSelected, SfPdfViewer.onAnnotationDeselected, SfPdfViewer.onAnnotationEdited and SfPdfViewer.onAnnotationRemoved callbacks.
Implementation
typedef PdfAnnotationCallback = void Function(Annotation annotation);