Modal - create variation using `dialog` element

Is this a new component or an extension of an existing one?
The Modal creates a ModalBox, which will have a variation in Core built using the <dialog> element.

Describe the feature
<dialog> provides functionality built into browsers that handles placing the modal on the top layer, handling keyboard focus, and providing a ::backdrop pseudoelement. Users should be able to opt in to this variant, which then probably does not need the separate Backdrop component, may not need to be placed in the DOM where it is now, and focus will be handled by the browser. A11y should be reviewed given that the dialog implicitly provides appropriate aria labeling.

https://developer.mozilla.org/en-US/docs/Web/HTML/Element/dialog

This issue is dependent on completion in core in https://github.com/patternfly/patternfly/issues/7296

Start by reviewing the existing React Modal and ModalBox behavior, then read the linked core issue 7296 and the MDN dialog documentation. Check how the Backdrop component and focus handling are currently used. Done means an opt-in dialog-based variation works with appropriate accessibility behavior and its interaction with Backdrop and DOM placement is resolved.