Introduce TxHash in Mempool

[bladyjoker]

Description

See #1444

TxHash identifies a transaction uniquely up to its contents (aux, witnesses etc). That's what makes it different to TxId which identifies a transaction up to its ledger effect (in Ledger that means the same TxBody and in Plutus that means the same TxInfo).

See prop_tx_id_valid_effect_is_same and prop_tx_hash_effect_is_same for their exact properties and how they differ.

In a nutshell, we anticipate we might want to diffuse transactions identified via TxHash for Leios as we want to make sure only the validated transactions are diffused. Since TxId obtained from node-A and node-B can have a different witness set and one might fail while the other doesn't.

DONE

• Add GenTxHash following the same pattern as GenTxId and wire the types and concrete implementations
• Align coding styles among different implementations (byron, shelley, test, hfc)
• Test properties of MempoolSnapshot and LedgerSupportsMempool
  • Specify the properties
  • Wire them in a concrete testsuite
• !!! Decide how to proceed given there's no immediate users of this feature and it's unclear there would be.
• Optimization: Pass around the serialized transaction to spare us from unnecessarily re-serializing.