Bug 311741 – Nesting requestClose() shouldn't fire multiple cancel events

• Status: NEW
• Component: DOM

[Luke Warlow]

```html
<dialog id="dialog">Some Dialog Content</dialog>

<script>
dialog.showModal();
dialog.oncancel = () => {
   dialog.requestClose();
};
dialog.requestClose();
</script>
```

This leads to a RangeError: Maximum call stack size exceeded. in WebKIt.

The spec prevents this through CloseWatcher machinery, we should add a guard to prevent this until CloseWatchers are finished and integrated with dialog.

[Luke Warlow]

Pull request: https://github.com/WebKit/WebKit/pull/62283