remove dependency of type support on rmw

[dirk-thomas]

Currently rosidl_typesupport_opensplice_cpp includes rmw/rmw.h for the symbol rmw_request_id_t (

rmw_opensplice/rosidl_typesupport_opensplice_cpp/resource/srv__type_support.cpp.template

Line 20 in 9c38019

#include <rmw/rmw.h>

). It does not in the package.xml (and should not) depend on the rmw package. Therefore it fails to build with the --isolated options.

Instead the definition for the request header should come from a low-level package which also needs to provide that for every language we aim to support (e.g. C, C++).

The definition to generate the request / response data structure including the header is in the rosidl_generator_dds_idl package (https://github.com/ros2/rosidl_dds/blob/32c4c22ab6784ed245d5399d37ac09628fde6d2b/rosidl_generator_dds_idl/rosidl_generator_dds_idl/__init__.py#L93-L120).

[dirk-thomas]

Considering to move the symbol to rosidl_generator_c.

[dirk-thomas]

Since it is not likely that we will move this single symbol I will close this for now.