Modal - create variation using dialog element

[srambach]

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 patternfly/patternfly#7296