Consider treating aria-hidden, non-tabbable, off screen elements hidden for everyone

Axe-core currently only considers `display none`, `visibility hidden` and `inert` elements as hidden to everyone. But content authors who ensure an element is off screen, not tabbable, not not in the accessibility tree have essentially done the same thing:

```html

.sr-only {
position: fixed;
top: 0;
left: 0;
width: 1px;
height: 1px;
overflow: hidden;
clip: rect(0 0 0 0);
}

I think elements like this should be considered hidden to everyone, and so should get ignored by rules unless they have `excludeHidden: false` set. This impacts quite a lot of rules, so probably something not something we want to put out in a patch.

Start by tracing how axe-core currently identifies display-none, visibility-hidden, and inert elements as hidden to everyone, then locate the shared logic used by rules honoring excludeHidden. Review the affected rules and their tests, and define completion as off-screen, non-tabbable, aria-hidden content being ignored by default while remaining included when excludeHidden is false.

Written by the indexing model from the issue text.