Validate the publishing package

[kettanaito]

Writing this down after a discussion with @acdlite (https://twitter.com/acdlite/status/1626616969024663552)

1. Validate required fields: name, version.
2. Validate static assets: main, typings, exports, files, and friends. All must point to existing files prior to a release.
3. Consider module compatibility validation (can what you publishing run in ESM? in CJS? in the browser?).
4. Warn against accidental publishing of wrong versions. Basically, a major version bump must always have an explicit confirmation step.