contextual role invalidations tests

[cookiecrook]

contextual role invalidations like orphaned roles outside their required context like a cell outside a table <div role="cell"> -> "undefined" (the resulting roles may be underspecified in some cases, so there may be implementation differences)

follow-on from #8

[cookiecrook]

In WPT PR 38925 (comment) @spectranaut mentioned this special case, which may apply to this issue:

Footer has different HTML-AAM mappings when in the context of main or not. Internally, Chrome uses the roles "FooterAsNonLandmark" and "Footer" to represent the difference (codepen example). I'd guess that WebKit doesn't need to have this distinction internally, though I'm not sure?

[rahimabdi]

@cookiecrook Self-assigning this one as well.