[Feat]: Add support for expand/collapse variant of Menu Item

[Westbrook]

trafficstars

Code of conduct

• [X] I agree to follow this project's code of conduct.

Impacted component(s)

Menu, Menu Item

Description of the requested feature

Spectrum will be adding support for this in the near future. Once it is spec'd, let's document the steps we'll need to take on here. Once it's shipped there are active consumers who are interested in adopting this functionality ASAP.

Mockups or screenshots

No response

Implementation notes or ideas

Is this something we can add to Menu Group rather than Menu Item so that it doesn't step on the toes of the fly out submenu?