Avoid repeating work in handle sig expansion/verification

[tinker-michaelj]

Summary
There are two simple ways to reduce the cost of signature verification in handleTransaction; both involve re-using information computed in Rationalization.execute().

• SwirldTransaction.getSignatures() acquires a lock and makes a defensive copy; the finalized List<TransactionSignature> can be set in a field on the scoped TxnAccessor.
• The AwareProcessLogic and InHandleActivationHelper will also need the payer and other-party required signing keys; these may also be recorded in a TxnAccessor field.