`.bytes()` method for "Opaque ByteArray" in the contract language

[papag00se]

On the Helios Lang side of the house - I am wondering if we can get a .bytes() on the "Opaque ByteArray" objects like MintingPolicyHash, DatumHash, etc. to make it easier to compare to a known ByteArray. Right now, the .serialize() functions wraps it in a CBOR tag.

.bytes(), .bytearray(), or .to_bytearray() all seem appropriate.

[christianschmitz]

I've added a .bytes getter to DatumHash, MintingPolicyHash, PubKeyHash, ScriptHash, StakingValidatorHash, ValidatorHash and TxId.

This is now available in 0.16.7