add type names, some more introspection functions

Almost there! Known issues:
* mangling/demangling is still wrong
* it necessarily has to run in the Cyclone default domain id: (1)
  Cyclone is today still limited to a single domain at a time; and (2)
  there is the "extra" participant that pops up here and there for
  creating guard conditions and waitsets without a node existing
* almost all query operations create a reader for a builtin topic and
  throw it away afterward, that might be a little excessive (on the other
  hand, those readers are pretty cheap, so using them as a throwaway
  reader is not so bad).

Still missing:
* get_service_names_and_types
* get_service_names_and_types_by_node

I haven't been able to actually try everything yet, so bugs are probably
lurking here-and-there.

rmw_cyclonedds_cpp/include/rmw_cyclonedds_cpp/TypeSupport.hpp

@@ -113,6 +113,7 @@ class TypeSupport
 public:
   bool serializeROSmessage(const void * ros_message, cycser & ser, std::function<void(cycser&)> prefix = nullptr);
   bool deserializeROSmessage(cycdeser & deser, void * ros_message, std::function<void(cycdeser&)> prefix = nullptr);
+  std::string getName ();
 
 protected:
   TypeSupport();

rmw_cyclonedds_cpp/include/rmw_cyclonedds_cpp/TypeSupport_impl.hpp

@@ -656,6 +656,12 @@ bool TypeSupport<MembersType>::deserializeROSmessage(
   return true;
 }
 
+template<typename MembersType>
+std::string TypeSupport<MembersType>::getName ()
+{
+  return name;
+}
+
 }  // namespace rmw_cyclonedds_cpp
 
 #endif  // RMW_CYCLONEDDS_CPP__TYPESUPPORT_IMPL_HPP_