[C++] Add skip method for var data fields without reading.

Author: mjpt777

sbe-tool/src/main/java/uk/co/real_logic/sbe/generation/cpp/CppGenerator.java

@@ -443,6 +443,24 @@ private void generateVarData(
             generateVarDataDescriptors(
                 sb, token, propertyName, characterEncoding, lengthToken, lengthOfLengthField, lengthCppType, indent);
 
+            new Formatter(sb).format("\n" +
+                indent + "    std::uint64_t skip%1$s()\n" +
+                indent + "    {\n" +
+                "%2$s" +
+                indent + "        std::uint64_t lengthOfLengthField = %3$d;\n" +
+                indent + "        std::uint64_t lengthPosition = sbePosition();\n" +
+                indent + "        %5$s lengthFieldValue;\n" +
+                indent + "        std::memcpy(&lengthFieldValue, m_buffer + lengthPosition, sizeof(%5$s));\n" +
+                indent + "        std::uint64_t dataLength = %4$s(lengthFieldValue);\n" +
+                indent + "        sbePosition(lengthPosition + lengthOfLengthField + dataLength);\n" +
+                indent + "        return dataLength;\n" +
+                indent + "    }\n",
+                propertyName,
+                generateArrayFieldNotPresentCondition(token.version(), indent),
+                lengthOfLengthField,
+                lengthByteOrderStr,
+                lengthCppType);
+
             new Formatter(sb).format("\n" +
                 indent + "    SBE_NODISCARD const char *%1$s()\n" +
                 indent + "    {\n" +