Create helper functions for ledger.Transaction to returned consumed inputs and produced outputs

[agaffney]

This is mostly needed to handle different behavior when a transaction is marked as "valid" or not. If it's valid, we want to return the standard TX inputs and outputs. If it's marked as not valid, we want to return the collateral inputs and/or collateral return value(s). We only want this on ledger.Transaction and not ledger.TransactionBody because we need information outside of the TX body to make the determination on validity.