refactor: test/bench: dedup Build{Crediting,Spending}Transaction()

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()).

src/Makefile.bench.include

@@ -39,6 +39,8 @@ bench_bench_bitcoin_SOURCES = \
   bench/lockedpool.cpp \
   bench/poly1305.cpp \
   bench/prevector.cpp \
+  test/lib/transaction_utils.h \
+  test/lib/transaction_utils.cpp \
   test/setup_common.h \
   test/setup_common.cpp \
   test/util.h \