Add radius foundation and tokens to storybook

[jameskoster]

What?

Adds radius foundations and tokens to storybook.

Why?

• Documenting the foundations creates an important point of reference for updating (or creating new) components and UIs.
• Documenting the tokens makes them more discoverable.

Testing Instructions

1. npm run storybook
2. Check out the new pages; 'Foundations / Design Language / Radius' and 'Tokens / Radius'

Foundations page	Tokens page

[github-actions]

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Co-authored-by: jameskoster <jameskoster@git.wordpress.org>
Co-authored-by: ciampo <mciampini@git.wordpress.org>
Co-authored-by: tyxla <tyxla@git.wordpress.org>
Co-authored-by: jasmussen <joen@git.wordpress.org>

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[jasmussen]

I think there's a question about the visual style we want to apply across these docs, it may be good to decide on a specific illustration style (which could be what you suggested, but it could also be this), and then roll it out consistently.

I think as a first draft this is fine. What do you think? Nice work.

[ciampo]

Rebased on top of latest changes, and pushed a couple of improvements / fixes.

In particular, I refactored the table so that it can be a more generic and work for both radius and elevation tokens. It's still a bit hacky, and we will definitely want to refine it (alongside other docs componentry)

[tyxla]

This is great work @jameskoster! 🚀

Left a few suggestions, but this is good to go anyway!

[ciampo]

@tyxla Since I was the last one to work on this PR (and I'm not sure about Jay's availability this week), I've addressed the remaining feedback.

Will merge as soon as CI checks pass ✅

[tyxla]

Thanks @ciampo and @jameskoster 🙌