org mode supports [1] setting the value attribute [2] of ordered list items to
change the numbering for the current and following items. Let's do the same. As
the attribute has no meaning for other types of lists [2] we'll just not
support it for those cases [3].
[1] https://orgmode.org/manual/Plain-Lists.html#Plain-Lists
[2] https://developer.mozilla.org/en-US/docs/Web/HTML/Element/li#attributes
[3]
Org mode seems to instead set the id attribute for e.g. unordered lists
starting with `[@\d+]\s` - but I don't really see the value in that and will
skip that for now.
21f1af7d48