Dialog should have an option for a close button in the corner

[merlinstardust]

Currently Dialog has no close buttons and you have to create them yourself. This is fine for when you want to have a cancel button or similar at the bottom of the modal because that often changes between implementations. Some people might put close or cancel or any number of things.

But most modals have an X in the corner for closing it as well as a button at the bottom. While I can add this myself, I am very confident that this is code that a lot of people are writing for their dialogs, and thus it should be built in to the dialog itself.

It doesn't have to be the default, but one should be able to <Dialog.Root showClosingCornerX> and have it appear.