vite: Add experimental support for Astro

[mechairoi]

Generate CSS when in the Astro build and SSR flag is enabled, similar to the React Server Component (#751).

Will fix #795

The reproduction of #795 seems to work correctly both of dev and build. (The build needs to move pages/index.css.ts outside of pages/ so that it is not treated as an entry point.)

[changeset-bot]

🦋 Changeset detected

Latest commit: b15c813

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@vanilla-extract/vite-plugin	Minor

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[arthur-fontaine]

I just updated and tested (with your pr) the reproduction to make the build and dev scripts run without error. I also fixed the style not fully applied on the cards.

[mattcompiles]

Thanks for the PR. Changes makes sense. Just a few comments around keeping the plugin as simple as possible.

[mechairoi]

Thanks for review. I have updated the PR.

[mattcompiles]

Happy with this as a code change.

@mechairoi Is it worth adding some docs for Astro users? Is it understood that Vite plugins generally work in Astro builds?

[mechairoi]

@mattcompiles I think it is better to add some docs. The reference is almost all the description of the Vite plugins in the Astro docs.

[mattcompiles]

@mechairoi I'll merge this for now. If you want to contribute some Astro specific docs then feel free to open another PR 😄