Fix the package.json exports and actually provide the typescript types

[MTRNord]

To test this you can do this:

1. Run yarn build
2. Go into a package
3. Run node ../../scripts/prepack.js
4. Run npx publint
5. Verify its happy

✔️ Checklist

• A changeset describing the change and affected packages (more info).
• Added or updated documentation.
• Tests for new functionality and regression tests for bug fixes.
• Screenshots or videos attached (for UI changes).
• All your commits have a Signed-off-by line in the message (more info).

[changeset-bot]

⚠️ No Changeset found

Latest commit: 377d8d2

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[MTRNord]

Also a good read for this is https://github.com/frehner/modern-guide-to-packaging-js-library on which I based this.