Dialog elements can be closed through a variety of mechanisms, sometimes developers want to have the ability to prevent closure. To achieve this dialogs fire a cancel event. Originally this was only fired via a close request (e.g. ESC key press), recently a `requestClose()` JS function was added which also fires the cancel event. The 'request-close' command brings that new ability to the declarative invoker commands API.
Invoker commands exposes existing dialog and popover functions to declarative HTML, for consistency we should also expose the new requestClose().
Explainers: https://github.com/whatwg/html/pull/11045