Returns the appearance state widget shows: its AS; without one, the field's value when the widget
has it as its on state, else Off.
public CosName GetAppearanceState(PdfWidgetAnnotation widget)
One of the field's widgets.
ISO 32000-2 §12.7.5.2.3: "the value of the AS key shall be used instead of the V key to determine which appearance to use".