Add function to convert CValidationState to a human-readable message

It is necessary to be able to concisely log a validation state.
Convert CValidationState to a human-readable message for logging.

(cherry picked from commit 9003c7cdd88402986e48ec126258fc10d6742fc7)

src/main.cpp

@@ -1715,6 +1715,14 @@ CAmount GetMinRelayFee(const CTransaction& tx, const CTxMemPool& pool, unsigned
     return nMinFee;
 }
 
+/** Convert CValidationState to a human-readable message for logging */
+static std::string FormatStateMessage(const CValidationState &state)
+{
+    return strprintf("%s%s (code %i)",
+        state.GetRejectReason(),
+        state.GetDebugMessage().empty() ? "" : ", "+state.GetDebugMessage(),
+        state.GetRejectCode());
+}
 
 bool AcceptToMemoryPool(
         const CChainParams& chainparams,