Define allowed ARIA attributes for div when a child of dl element

[scottaohara]

Allowing div as a child of dl has introduced some oddities with AT understanding the contents of a dl element correctly. This seems mostly an issue for AT to resolve, and largely they have as far as I recall, Browsers generally appear to be exposing their accessibility trees appropriately (more testing needed).

However, as I was reminded by whatwg/html#7347, I think we need to make it absolutely clear that if a div is acting as a styling/grouping container for dt and dd elements, it must not be allowed any ARIA roles outside of presentation/none, and no global aria-* attributes. Otherwise, this would break the already awkward mappings/user experience of the dl element.

[scottaohara]

Testing the following:

<dl>
  <div role=navigation>
    <dt>test</dt>
    <dd>...</dd>
  </div>
</dl>

only axe presently flags that this is incorrect. so seems a good idea to get this into the spec to get other checkers to correctly flag this error.

[scottaohara]

likely straight forward adding of a mention to the div allowances column stating that if a direct child of a dl then no allowed roles other than none/presentation.

[scottaohara]

this was closed by merging of #403