feat!: Remove unnecessary Dialog wrapper

[alimpens]

Describe the pull request

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What

It removes an unnecessary wrapper in Dialog. It also updates some tests.

Why

It simplifies the Dialog component and groups all sizing CSS rules in the same class.

How

By deleting the wrapper and moving all CSS rules to the root class.

Checklist

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• Add or update unit tests
• Add or update documentation
• Add or update stories
• Add or update exports in index.* files
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Additional notes

Some things I ran into while doing this work, maybe we should look into them in a separate ticket:

• Should we set a min-block and min-inline size as well, like Utrecht? Maybe we don't want it to shrink beyond a certain point? This is especially an issue for longer body content, that can become so small it's invisible.
• What color should the backdrop be? It's currently a hex value, but what is it based on? Is it a brand color with lower opacity?
• WAI-ARIA recommends returning the focus to the button that opens the dialog on close. I think we should document that.