`DialogV2` has incorrect names for width values

[iansan5653]

The new Dialog component has a width prop:

https://github.com/primer/react/blob/f9eae58360ebaac9f3ada777e11f954d3013782a/packages/react/src/Dialog/Dialog.tsx#L114-L121

These size names do not match the Primer overlay primitives.

It should be:

• xsmall: 192px
• small: 320px
• medium: 480px
• large: 640px
• xlarge: 960px

Currently the only way to make an actual xlarge dialog is to set the width explicitly via sx.

[broccolinisoup]

Thanks @iansan5653 for raising this issue. I liked it to the epic (Staff only link) that we do all the dialog work. Let us know if you have any concern with it 🙌