eosjs-ecc methods and migration (release/21.0.x branch)

[bradlhart]

Change Description

Following feedback and requests, the ecc helper functions have been renamed to match the eosjs-ecc methods where possible. A private key generation method has also been added, as well as a PublicKey.toLegacyString() method for backwards compatibility.

Lastly, an ecc exported object is available with all the functions eosjs-ecc has that utilizes the new functions.

Second PR to cherry pick commits to release/21.0.x branch

API Changes

• API Changes

Changed:
sign, verify, and recover now have the argument shouldHash that by default is set to true. These functions will hash the data given but can accept already hashed data with shouldHash = false
PublicKey.validate was renamed to PublicKey.isValid
Signature.recoverPublicKey was renamed to Signature.recover

New:
PrivateKey.toLegacyString: Convert private key to Legacy EOSIO-format private key
PrivateKey.isValid: Validate a private key
PublicKey.toLegacyString: Convert public key to Legacy EOSIO-format public key
generateKeyPair: Utilizes the elliptic package to generate a public and private key pair. This function should only be used in secure environments and requires an environment variable to be set to confirm that the environment is secure.
sha256: An exported sha256 function from the elliptic package

Documentation Additions

• Documentation Additions