Copy type_description_interfaces structs to runtime_c/cpp

[emersonknapp]

Depends on ros2#729
Staging this PR for visibility against PR-in-review. It will have to be reopened against ros2 when ros2#729 is merged.

Provides usable runtime types for use by dynamic types and codegen for type descriptions.

Provides a script that does the copying and modification in a single invocation - all added headers and sources in this change have not been touched by hand and never should be.

For the reviewer - most importantly see scripts/copy_type_description_generated_sources.bash

[methylDragon]

I think it's a good idea to commit the generated files since version control can track if any changes to the output are made (either from changes from the rosidl code generation, or something else) (though I'm not sure who would be continually rebuilding and checking)

(Well that and users wouldn't be running the script anyway...)

LGTM

[methylDragon]

That said, I'm not sure if it would be better if the script was invoked in the CMakeLists instead. That would ensure that any future changes to rosidl would update the generated code (though there's the slight danger that errors in env var setting could lead to some pretty nasty rm calls.)

I don't have a preference for this though.

[emersonknapp]

That said, I'm not sure if it would be better if the script was invoked in the CMakeLists instead

This approach isn't possible - rosidl_runtime_c[pp] are dependencies of type_description_interfaces - there's no way to know at their build time that there even is a build directory anywhere for type_description_interfaces - they may be in a standalone workspace all by themselves. It has to be a checked-in copy updated by something (for now a human) outside the CMake/colcon build process.

[methylDragon]

Ah.. okay