Gets the page's annotations, in the order of its Annots array, each typed by its subtype.
public IReadOnlyList<PdfAnnotation> Annotations { get; }
ISO 32000-2 §7.7.3.3, Table 31 (Annots), and §12.5. The list is built on first use and rebuilt when the page's
Annots entry or array, or an annotation's Subtype, changes, or an object is added or removed (§7.3.10); each annotation is a live view over its dictionary, and the same dictionary always
gives the same instance. An element that is not an annotation dictionary is skipped; one listed twice appears twice. An
Annots entry on a page tree node above the page, which is not inheritable, is used as viewers use it.
Deviations in the array are recorded in Diagnostics when the list is built.