Add constant scriptCode policy in non-segwit scripts

This disables OP_CODESEPARATOR in non-segwit scripts (even in an unexecuted branch), and makes a positive FindAndDelete result invalid. This ensures that the scriptCode serialized in SignatureHash() is always the same as the script passing to the EvalScript.

src/script/script_error.cpp

@@ -89,6 +89,10 @@ const char* ScriptErrorString(const ScriptError serror)
             return "Witness provided for non-witness script";
         case SCRIPT_ERR_WITNESS_PUBKEYTYPE:
             return "Using non-compressed keys in segwit";
+        case SCRIPT_ERR_OP_CODESEPARATOR:
+            return "Using OP_CODESEPARATOR in non-witness script";
+        case SCRIPT_ERR_SIG_FINDANDDELETE:
+            return "Signature is found in scriptCode";
         case SCRIPT_ERR_UNKNOWN_ERROR:
         case SCRIPT_ERR_ERROR_COUNT:
         default: break;