refactor(project): remove theme-preval.js

[joshblack]

The theme-preval.js file is used alongside babel-plugin-preval to generate an object containing all the tokens and values from @primer/primitives. For an example of its output, see: https://unpkg.com/browse/@primer/react@35.25.1/lib-esm/theme-preval.js

This approach introduces some limitations, namely that:

• It couples our project to babel and makes it difficult to switch to alternative bundlers (like TypeScript, esbuild, swc, etc)
• It mixes CommonJS with ESM in a way that makes it difficult to use tools like api extractor to analyze our declaration files
• It generates the largest file in our bundle at ~149kB uncompressed, 13.8kB gzip

The experiment here looks into removing our dependency on preval so that:

• We can explore other bundlers in the future
• We can simplify our bundler and babel setup by removing babel-plugin-preval along with transforms we use for mapping the emitted CommonJS to ESM
• We can rely on tools like api extractor to extract types instead of manually preparing them for documenting and for CI tooling

From a user perspective, this change should not be noticeable. Even though @primer/primitives is currently emitting CommonJS, the size difference should be minimal as we were including the package contents in the emitted theme-preval.js file

[changeset-bot]

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Latest commit: 3f03daa

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[github-actions]

size-limit report 📦

Path	Size
dist/browser.esm.js	115.85 KB (+19.87% 🔺)
dist/browser.umd.js	117.67 KB (+21.17% 🔺)

[joshblack]

cc @colebemis would love your feedback here! 👀

[colebemis]

Since we're not using polished, I think removing theme-preval.js is a good idea 👍 This will make all our lives a lot easier. No more cache issues! 🎉