Previously list continuation counters were kept per list level
only, so a list with `text:continue-numbering="true"` continued
from whatever list last occupied that level, even one with a
different list style, and the first such list started at 0.
Word sets this attribute on every list, so exported documents
got very odd start numbers.
Now counters are keyed by list style name and level (nested lists
without a style name inherit their parent's), numbering only
continues from a previous list with the same style, lists with
nothing to continue from use the style's start value, and the
counters for deeper levels are reset when a new list item starts.
Closes#9595.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
