This change implements spec-conformant computation of default ARIA roles
for elements whose expected default role depends on the element’s
context — specifically, either on the element’s ancestry, or on whether
the element has an accessible name, or both. This affects the “aside”,
“footer”, “header”, and “section” elements.
Otherwise, without this change, “aside”, “footer”, “header”, and
“section” elements may unexpectedly end up with the wrong default roles.
