[C++] Capture acting block length and use it with << operator. Issue aeron-io#839.

Author: mjpt777

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

@@ -1911,6 +1911,7 @@ private static CharSequence generateConstructorsAndOperators(final String classN
  " m_bufferLength(bufferLength),\n" +
  " m_offset(offset),\n" +
  " m_position(sbeCheckPosition(offset + actingBlockLength)),\n" +
+ " m_actingBlockLength(actingBlockLength),\n" +
  " m_actingVersion(actingVersion)\n" +
  " {\n" +
  " }\n\n" +
@@ -1946,6 +1947,7 @@ private CharSequence generateMessageFlyweightCode(final String className, final
  " std::uint64_t m_bufferLength = 0;\n" +
  " std::uint64_t m_offset = 0;\n" +
  " std::uint64_t m_position = 0;\n" +
+ " std::uint64_t m_actingBlockLength = 0;\n" +
  " std::uint64_t m_actingVersion = 0;\n\n" +
 
  " inline std::uint64_t *sbePositionPtr() SBE_NOEXCEPT\n" +
@@ -2518,8 +2520,12 @@ private void generateDisplay(
  "friend std::basic_ostream<CharT, Traits> & operator << (\n" +
  " std::basic_ostream<CharT, Traits> &builder, %1$s _writer)\n" +
  "{\n" +
- " %1$s writer(_writer.m_buffer, _writer.m_offset,\n" +
- " _writer.m_bufferLength, _writer.sbeBlockLength(), _writer.m_actingVersion);\n" +
+ " %1$s writer(\n" +
+ " _writer.m_buffer,\n" +
+ " _writer.m_offset,\n" +
+ " _writer.m_bufferLength,\n" +
+ " _writer.m_actingBlockLength,\n" +
+ " _writer.m_actingVersion);\n\n" +
  " builder << '{';\n" +
  " builder << R\"(\"Name\": \"%1$s\", )\";\n" +
  " builder << R\"(\"sbeTemplateId\": )\";\n" +