crypto: allow deriving public from private keys

This change allows passing private key objects to
crypto.createPublicKey, resulting in a key object that represents a
valid public key for the given private key. The returned public key
object can be used and exported safely without revealing information
about the private key.

PR-URL: https://github.com/nodejs/node/pull/26278


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>