Gets the field's widget annotations, in Kids order: the field dictionary itself when it is merged with its only widget.
Each is the instance the page holding it lists; a widget no page lists has no Page.
public IReadOnlyList<PdfWidgetAnnotation> Widgets { get; }
ISO 32000-2 §12.7.2, §12.7.4.1 (Table 226, Kids) and §12.5.6.19. A kid whose subtype is not Widget is not listed.