Word represents "restart numbering" on a style-based list by pointing
only the first item of the restarted list at a new `numId` that shares the
original list's abstract numbering definition but carries a
`w:startOverride`; the remaining items keep using the original `numId`.
Pandoc keyed list continuation and grouping on the `numId`, so the
restarted items continued the stale count from the earlier list (and
were split into a separate ordered list with the wrong start).
Key continuation and grouping off the `abstractNumId` instead (the real
running counter in Word), and treat `startOverride` as a restart that
resets the count.
Closes#8367.
Co-Authored-By: Claude <noreply@anthropic.com>
