Add error when running build script after prepack (#55914)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55914

Introduce a clear error message if running `yarn build` again after `yarn prepack` (which will have applied the `"publishConfig"` field to each `package.json`, just ahead of publishing to npm). This state should never happen in CI or local dev, but can occur if repeat-running `yarn test-release-local` without `yarn test-release-local-clean`.

Introducing a validation error is preferable over making this idempotent (logic would be complex + fragile) for this rare + out-of-design edge case.

Changelog: [Internal]

Reviewed By: alanleedev

Differential Revision: D95215735

fbshipit-source-id: 5a9be44f0d0ae1f2721eed2b11088466a4ff7f72