feat: support private keys

[fisker]

npm offical package read-package-json and popular package read-pkg and read-pkg-up, add some private keys to json, like _id.

This PR make those private keys always at bottom. so we can easy read -> sort -> write, like this

const {path, packageJson} = await readPkg()
const sorted = sortPackageJson(packageJson)
await writePkg(path, sorted)

[keithamus]

🎉 This PR is included in version 1.33.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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