Add a11y-support check for nested ownership

[WilcoFiers]

<div role="menu">
  <div><div role="menuitem">Item 1</div></div>
  <div role="presentation">
    <div role="menuitem">Item 1</div>
  </div>
</div>

Axe-core flags these correctly as failures. What it does not do however is report that these are failures because owning descendants isn't widely supported. We should add a check that can distinguish between "no owner/owned element at all" and "an owner/owned element, but done in a way that isn't accessibility supported".

I don't yet have a proposal on how to do this, but I'm sure we can come up with something. The newly introduced aria.getOwner() could help with that, and should probably get a few "unsupported" feature flags so that we can make this configurable.

[straker]

With the changes we made to required-children, this code no longer throws an error.

[straker]

Need to do some testing to verify if the <div> wrapping the first menuitem is a problem for screen readers.