Add test: Get current page number for direct quote

This test is described and motivated here

### Test
If ePub readers cannot support getting the current pagination number of a passage, as it would appear in a book or journal article (e.g., PDF) available to sighted readers, then there is a problem.

As this is an essential task in academia, the mechanism should be efficient (i.e., fast), effective (i.e., free from risk of error), and satisfying to screen reader users. These are the 3 attributes of usability according to the International Standards Organization's standard for Ergonomics of human-system interaction — [Part 11: Usability: Definitions and concepts](https://www.iso.org/obp/ui/#iso:std:iso:9241:-11:ed-2:v1:en) (ISO 9241-11:2018). Search for labels 3.1.12, 3.1.13, and 3.1.14 for definitions of effectiveness, efficiency, and satisfaction.

### Motivation
This issue was drawn to my attention by blind undergraduate, masters, and PhD students, as well as a faculty member. It was unequivocally a problem and a very significant one at that. It affects how blind users formulate their thoughts and share their knowledge in higher education.

In post-secondary settings, from under grad to full faculty, students and researchers are expected to quote journal articles or books and include page numbers. While some publishing manuals may have some esoteric exceptions that don't require page numbers, this is just one of those extremely powerful norms that if not followed will have souring effects on a person's academic path or career.

Until the day comes when the norm of having page numbers with direct quotes is no longer expected of anyone in academia, then we need to ensure blind screen reader users can get page numbers without being slowed down an iota.

The issue names no files, tests, or entry points. Start by locating the repository’s existing EPUB accessibility tests and how they describe reading-system capabilities; define a reproducible test for retrieving the current page number for a passage, with completion requiring an efficient, accurate, screen-reader-usable result.

Written by the indexing model from the issue text.