prototypes used in src/test/script_tests.cpp:

• CMutableTransaction BuildCreditingTransaction(const CScript& scriptPubKey, int nValue = 0);
• CMutableTransaction BuildSpendingTransaction(const CScript& scriptSig, const CScriptWitness& scriptWitness, const CTransaction& txCredit);

prototypes used in bench/verify_script.cpp:

• CMutableTransaction BuildCreditingTransaction(const CScript& scriptPubKey);
• CMutableTransaction BuildSpendingTransaction(const CScript& scriptSig, const CMutableTransaction& txCredit);

The more generic versions from the script tests are moved into a new file pair
transaction_utils.cpp/h and the calls are adapted accordingly in the
verify_script benchmark (passing the nValue of 1 explicitely for
BuildCreditingTransaction(), passing empty scriptWitness explicitely and
converting txCredit parameter to CTransaction in BuildSpendingTransaction()).

This is a backport of Core PR17183

The benchmark in question was deleted because segwit dependent, but it may be a good time to resurrect it.