feat(cli): add exports field

[chenjiahan]

Summary

• Add exports field to the @rspack/cli package, align with @rspack/core and @rspack/dev-server.
• Use sort-package-json to sort the package.json file.

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[hardfist]

what will consume @rspack/cli js API?

[chenjiahan]

@hardfist Only a few public API, such as defineConfig and definePlugin:

// rspack.config.ts
import { defineConfig } from '@rspack/cli';

I add the exports field to prevent the internal modules of @rspack/cli from being mistakenly consumed by users.