For annotations on EPUBs, text position selectors can only be validly compared
when they come from annotations made on the same EPUB Content Document. For
annotations that come from different content documents, it is necessary to first
compare the ordering of the content documents using CFIs, and then compare text
positions.

The use of `Number.POSITIVE_INFINITY` with replaced with
`Number.MAX_SAFE_INTEGER` when handling annotations without positions, as
`Math.sign(MAX_SAFE_INTEGER - MAX_SAFE_INTEGER)` is 0 (ie. treat two annotations
with missing positions as having the same position), but
`Math.sign(POSITIVE_INFINITY - POSITIVE_INFINITY)` is NaN.