Check for use of aria-hidden paired with hidden=until-found

[scottaohara]

ARIA in HTML is updating to indicate that the use of aria-hidden=true on an element that also has the hidden=until-found attribute needs to be treated as a MUST NOT author error.

Using both together means that someone could find the hidden content using a browser in-page search, but the revealed previously hidden content will now be visually hidden, but still inaccessible to people using AT.