[build] Add several util units

Adds the following util units and adds them to libbitcoin_util:

- `util/url.cpp` takes `urlDecode` from `httpserver.cpp`
- `util/error.cpp` takes `TransactionErrorString` from
  `node/transaction.cpp` and `AmountHighWarn` and `AmountErrMsg` from
  `ui_interface.cpp`
- `util/fees.cpp` takes `StringForFeeReason` and `FeeModeFromString` from `policy/fees.cpp`
- `util/rbf.cpp` takes `SignalsOptInRBF` from `policy/rbf.cpp`
- 'util/validation.cpp` takes `FormatStateMessage` and `strMessageMagic` from 'validation.cpp`

src/node/transaction.cpp

@@ -6,38 +6,13 @@
 #include <consensus/validation.h>
 #include <net.h>
 #include <txmempool.h>
+#include <util/validation.h>
 #include <validation.h>
 #include <validationinterface.h>
 #include <node/transaction.h>
 
 #include <future>
 
-std::string TransactionErrorString(const TransactionError err)
-{
-    switch (err) {
-        case TransactionError::OK:
-            return "No error";
-        case TransactionError::MISSING_INPUTS:
-            return "Missing inputs";
-        case TransactionError::ALREADY_IN_CHAIN:
-            return "Transaction already in block chain";
-        case TransactionError::P2P_DISABLED:
-            return "Peer-to-peer functionality missing or disabled";
-        case TransactionError::MEMPOOL_REJECTED:
-            return "Transaction rejected by AcceptToMemoryPool";
-        case TransactionError::MEMPOOL_ERROR:
-            return "AcceptToMemoryPool failed";
-        case TransactionError::INVALID_PSBT:
-            return "PSBT is not sane";
-        case TransactionError::PSBT_MISMATCH:
-            return "PSBTs not compatible (different transactions)";
-        case TransactionError::SIGHASH_MISMATCH:
-            return "Specified sighash value does not match existing value";
-        // no default case, so the compiler can warn about missing cases
-    }
-    assert(false);
-}
-
 TransactionError BroadcastTransaction(const CTransactionRef tx, uint256& hashTx, std::string& err_string, const CAmount& highfee)
 {
     std::promise<void> promise;

src/node/transaction.h

@@ -8,20 +8,7 @@
 #include <attributes.h>
 #include <primitives/transaction.h>
 #include <uint256.h>
-
-enum class TransactionError {
-    OK, //!< No error
-    MISSING_INPUTS,
-    ALREADY_IN_CHAIN,
-    P2P_DISABLED,
-    MEMPOOL_REJECTED,
-    MEMPOOL_ERROR,
-    INVALID_PSBT,
-    PSBT_MISMATCH,
-    SIGHASH_MISMATCH,
-};
-
-std::string TransactionErrorString(const TransactionError error);
+#include <util/error.h>
 
 /**
  * Broadcast a transaction