Add exports field to packages with multiple entrypoints

[markdalgleish]

Fixes the following issue: https://github.com/markdalgleish/preconstruct-node-esm-import-issue. To see the fix working, you can run this repro locally and manually apply the diff seen in this PR to node_modules/@vanilla-extract/sprinkles/package.json.

Related issue on Preconstruct: preconstruct/preconstruct#432

More detail about the exports field and its conditional syntax: https://webpack.js.org/guides/package-exports

I ran into this issue because the Sprinkles runtime was being consumed within an ESM package (i.e. "type": "module") and Node.js doesn't allow directory imports in ESM mode. Instead, all nested import paths need to be explicitly defined in the exports field.

[changeset-bot]

🦋 Changeset detected

Latest commit: ed12ec0

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

This PR includes changesets to release 12 packages

Name	Type
@vanilla-extract/css	Patch
@vanilla-extract/dynamic	Patch
@vanilla-extract/recipes	Patch
@vanilla-extract/sprinkles	Patch
@vanilla-extract/webpack-plugin	Patch
@fixtures/features	Patch
@fixtures/low-level	Patch
@fixtures/recipes	Patch
@fixtures/sprinkles	Patch
@fixtures/themed	Patch
@fixtures/unused-modules	Patch
vanilla-extract-example-webpack-react	Patch

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