Support the HTML inert attribute

[WilcoFiers]

In Chrome 102 we're expecting the inert attribute to be supported. This has a number of implications for axe-core. I think we'll need to update a number of internal methods to understand this new attribute. I think since it's not going to be available to a number of other browsers yet a new rule that fails the use of inert unless it's polyfilled is probably also useful here.

[straker]

This has full browser support without a polyfill except for Firefox, which has it supported in the latest nightly. https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/inert#browser_compatibility

[padmavemulapati]

Validated with the latest axe-core develop branch code base,
inert attribute is a boolean value that, when present, makes the browser "ignore" user input events for the element, including focus events and events from assistive technologies.
Ex:

When not passing inert attribute for the below code snippet to fail for aria-hidden-focus , it is failing.

<div  id="violation" aria-hidden="true">
    <a href="/" style="position:absolute; top:-999em">Link</a>
  </div>

but when we have inert attribute for the same this is allowing.

<div inert id="violation" aria-hidden="true">
    <a href="/" style="position:absolute; top:-999em">Link</a>
  </div>