Pure render function on a *pdftext.Doc with no I/O: the whole text with
page markers when it fits, otherwise a map (title, outline with page
numbers, leading pages and how to ask for more), a page range, or grep
results with page numbers. Every length is in runes.
Co-Authored-By: ornith-1.5-35b-a3b <ornith-1.5-35b-a3b@llama.cpp.invalid>
