Implement safe API for ecrecover for env

[austinabell]

ecrecover is used to recover a secp256k1 public key from a secp signature and a 32-byte message hash that was signed. This probably doesn't have a ton of use cases in NEAR due to the fact that tooling supports ed25519 keys, but maybe for niche use cases this could be useful to sign messages off-chain and be able to submit and verify on-chain later.