Definition of "Programmatically Hidden" doesn't handle `aria-owns` correctly.

[Jym77]

Namely, the definition states that an element is hidden if it has an ancestor with aria-hidden, but this is not true if it is also pointed to by an aria-owns from an non-hidden element.

Interactions between aria-owns and aria-hidden are a bit tricky, ARIA is having some clarification on the topic. We might want to wait until the clarifications settle down upstream before making changes in our definition.