fix: include content in css sourcemap when extracting

[stipsan]

Hi 👋

Without source map contents included (which is the default behavior of rollup sourcemaps) it makes them less useful.

For example if you explore the app.css and app.css.map for the fixtures/react-library-example workspace on [https://evanw.github.io/source-map-visualization] the mappings lead to empty files:

With this PR the mappings now preserve the CSS that were initially omitted:

Richer sourcemaps are especially useful when vanilla extract is the first step, and later on lightningcss, cssnano or postcss is operating on the extracted CSS asset. In those scenarios it's helpful to know what the CSS looked like before it was optimized and possibly deduped 😌

Thanks so much for #1604 and #1616 btw. At Sanity we've decided to move away entirely from styled-components; vanilla-extract is shaping up to become its replacement. Since our tooling is leaning heavily on rollup, with the long term goal of moving to rolldown, these recent improvements were helpful and appreciated ❤

[changeset-bot]

🦋 Changeset detected

Latest commit: 28e293e

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/rollup-plugin	Patch

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[askoufis]

Thanks for the fix! Appreciate the example and explanation.