Remove Hidden Information counted and removed as a comment every
annotation that was not a link, widget, pop-up, file attachment or
redaction mark, so a Comments-only cleanup also deleted Watermark,
PrinterMark, TrapNet, Screen, Movie, RichMedia and 3D annotations.
Use pdfcraft_annot::is_comment_subtype, which the comments list already
uses, and keep excluding file attachments (removed with Attachments)
and redaction marks as before.
Adds tests::removing_comments_keeps_annotations_that_are_not_comments,
which fails before this change.
Marco Arnulfo
9593ff7419