LibWeb: Implement dialog.requestClose()

[lukewarlow]

Depends on #3354

See https://html.spec.whatwg.org/multipage/interaction.html#dom-closewatcher-requestclose

Can manually test using https://wpt.live/html/semantics/interactive-elements/the-dialog-element/dialog-requestclose.html where it passes all tests.

If I import the test it's flaky and sometimes fails on test runner.

[lukewarlow]

The test passes when running in the browser and when imported, but if I run with the test runner I get same error as CI, it seems something is flaky and can lead to two close events being fired (at least according to the test)

It makes use of abort signal and I'm wondering if there's an issue with Ladybird's impl?

[github-actions]

Your pull request has conflicts that need to be resolved before it can be reviewed and merged. Make sure to rebase your branch on top of the latest master.

[lukewarlow]

Going to move some of these changes to a PR that introduces all the popover=hint changes at once as they're orthogonal to this change.

[github-actions]

Your pull request has conflicts that need to be resolved before it can be reviewed and merged. Make sure to rebase your branch on top of the latest master.