Runtime Interface Reflection: rosidl_dynamic_typesupport_fastrtps

[methylDragon]

This PR is part of the runtime interface reflection subscription feature of REP-2011: ros2/ros2#1374
After merging this, merge:

• Add rosidl_dynamic_typesupport_fastrtps repo ros2#1392

Description

This PR provisions a serialization support library implementation fulfilling the interface laid out in rosidl_dynamic_typesupport

TODO

• Add a few missing interfaces
• Migrate to use the type_description_interfaces package instead of the internal type description struct

[wjwwood]

This generally lgtm, I removed a lot of my staged comments as they revolved around either:

• print functions, which we've agreed to remove before merging, and
• how double-pointers and allocations in the functions are used a lot when it's not necessary, which we've agreed to fix in follow up pr's if there's time

So I will approve this with the print functions removed.

[methylDragon]

This generally lgtm, I removed a lot of my staged comments as they revolved around either:

• print functions, which we've agreed to remove before merging, and
• how double-pointers and allocations in the functions are used a lot when it's not necessary, which we've agreed to fix in follow up pr's if there's time

So I will approve this with the print functions removed.

0f5ae5a

Print functions removed 😬