[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/validation.cpp

@@ -39,8 +39,10 @@
 #include <ui_interface.h>
 #include <undo.h>
 #include <util/moneystr.h>
+#include <util/rbf.h>
 #include <util/strencodings.h>
 #include <util/system.h>
+#include <util/validation.h>
 #include <validationinterface.h>
 #include <warnings.h>
 
@@ -259,8 +261,6 @@ std::atomic_bool g_is_mempool_loaded{false};
 /** Constant stuff for coinbase transactions we create: */
 CScript COINBASE_FLAGS;
 
-const std::string strMessageMagic = "Bitcoin Signed Message:\n";
-
 // Internal stuff
 namespace {
     CBlockIndex *&pindexBestInvalid = g_chainstate.pindexBestInvalid;
@@ -462,15 +462,6 @@ static void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age)
         pcoinsTip->Uncache(removed);
 }
 
-/** Convert CValidationState to a human-readable message for logging */
-std::string FormatStateMessage(const CValidationState &state)
-{
-    return strprintf("%s%s (code %i)",
-        state.GetRejectReason(),
-        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
-        state.GetRejectCode());
-}
-
 static bool IsCurrentForFeeEstimation() EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     AssertLockHeld(cs_main);