In 3.0, we made the decision to export all types from the main package
export (e.g. `payload/types` => `payload`). This improves type
discoverability by IDEs and simplifies importing types.
This PR does the same for our db adapters, which still have a separate
`/types` subpath export. While those are kept for
backwards-compatibility, we can remove them in 4.0.
