[dialog] CloseWatcher support?

## Summary

Native `` supports this API. Maybe we should, too. See https://developer.mozilla.org/en-US/docs/Web/API/CloseWatcher.

## Examples in other libraries

- https://github.com/ariakit/ariakit/issues/3243
- https://github.com/adobe/react-spectrum/issues/5531

## Motivation

Make it so that the state of the UI can be more easily navigated too.

There is a big UX problem with this, though: https://github.com/mui/base-ui/pull/3680#issuecomment-3826167764.
I find it interesting to have an issue so other people can find it, but otherwise, as a user, I would personally prefer that this didn't exist because I don't trust it will ever get adopted by enough websites I use daily. (So only valuable for Android apps that are webviews, a niche market)