Text in rendering mode 3 (invisible: a scanned page's searchable OCR layer) was dropped with no
warning, so a scanned PDF opened and saved again lost its searchable text without a hint. The
import now reports INVISIBLE_TEXT_NOTE when it leaves such text out, for type and outlines alike.
Keeping the text needs a kind of type that is kept but not drawn, and the PDF writer (krilla, in
craft-libs) to write it with `3 Tr`; its text API has fill, stroke and fill-and-stroke only.