Add Group role as supported required children element for ListBox role (1.2 specification update)

The WAI-ARIA 1.2 spec adds the `group` role containing `option` children as a supported required owned elements of `listbox` ([refer to the draft spec reference](https://www.w3.org/TR/wai-aria-1.2/#listbox)).

We leverage this implementation in our platform since it is the recommended way to emulate a `` with `` grouping. ([refer to the W3C ListBox with grouped options sample](https://w3c.github.io/aria-practices/examples/listbox/listbox-grouped.html))

While not completely thorough (verified only Win10 platform), an investigation of support of the 1.2 ListBox pattern seems good overall among common browser and screen reader combos.

We think that axe-core should detect the `group` role with `option` as a valid required owned elements for `listbox`, as per the 1.2 specification updates to reflect current support and specification signal.

Currently, running axe-core (via Accessibility Insights for this issue report), there is errors reported for the [ListBox with grouped options sample](https://w3c.github.io/aria-practices/examples/listbox/listbox-grouped.html).

Expectation: No error reported.

Actual: Reports the following error:
Required ARIA child role not present: option

Motivation: The group role support is actually well supported in all browser when in a listbox role. While the readout isn't consistent across platform, it does show relationship and groupings. As such, allowing this role today, while technically in a draft spec, would reflect current support and specification signal.

axe-core version: 4.0.1
from Accessibility Insight version 2.21.1

Browser and Assistive Technology versions
Edge 85 + Narrator (excellent)
Chrome 85 + JAWS 2020 (excellent)
Firefox 80 + NVDA 2020.1 (great)
IE 11 + Narrator (ok)