Add exports field to packages

[emmatown]

This adds the exports fields to the packages using Preconstruct, the only ways this really affects consumers is that:

• Entrypoints that are not at the root of a package can be imported from Node ESM (the root could be imported previously)
• In Node, some bundlers and TypeScript's "moduleResolution": "nodenext", anything that isn't specified in the exports will not be allowed to be imported outside the package. For example, people won't be able to reach into the dist directory and import some random file. (Note this also applies in CommonJS, not only ESM)

For people who have seen the exports field before, you might be expecting to see the import condition used. We are intentionally not using it here as we don't ship ESM for Node. We do use the module condition though which is respected by some bundlers (but not Node).

[vercel]

The latest updates on your projects. Learn more about Vercel for Git ↗︎

Name	Status	Preview	Updated
keystone-next-docs	✅ Ready (Inspect)	Visit Preview	Oct 31, 2022 at 2:18AM (UTC)

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit c10e9c0:

Sandbox	Source
@keystone-6/sandbox	Configuration