Replace index.d.ts with generated type definitions

[colebemis]

Problem

Primer React was originally released without TypeScript type definitions, making it difficult for engineers to consume the library in TypeScript applications. In July 2019, we created an ambient declaration file (index.d.ts) file to provide type definitions for TypeScript applications without having to rewrite Primer React components in TypeScript.

index.d.ts has been an effective stopgap, enabling teams to build complex applications with Primer React and TypeScript. However, because index.d.ts is disconnected from the implementation code, we've struggled to keep the type definitions up-to-date and accurate, as evidenced by many TypeScript bug reports. As the library continues to grow in size and complexity, manually maintaining type definitions will become unsustainable.

Solution

Now that all our components have been rewritten in TypeScript, we can use the TypeScript compiler to generate type definitions instead of manually maintaining an ambient declaration file. This PR removes our manually maintained index.d.ts file and updates the package.json to reference the generated type definitions.

Checklist

• Export prop types from index.ts 21c806c
• Update typings field in package.json to reference generated type definitions bab3e96
• Test generated type definitions in an application
• Fix type errors
• Delete index.d.ts
• Write changeset

[changeset-bot]

🦋 Changeset detected

Latest commit: db47820

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

This PR includes changesets to release 1 package

Name	Type
@primer/components	Major

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[dgreif]

Sorry, didn't realize this was a Draft PR before I started reviewing 😄 . Ignore anything you already have fixed up

[dgreif]

Awesome work, this is a major accomplishment! 🏆 🚀