To reduce the chances of mis-anchoring quotes, check for a context match
before stopping early. This helps when the quote is a word or phrase
that is common in the document and the position hint is wrong, which can
occur if the quote selector was created when using a different PDF
viewer or version of PDF.js, which exacts text differently.

For quotes captured at the start or end of a page we expect a mismatch
in the prefix and suffix respectively because quote selectors can currently
capture parts of the surrounding pages / DOM in `describe`, but when
anchoring we only search for matches in one page of text at a time.