Add type_description struct conversion utils

[methylDragon]

This adds the rclcpp analogue of https://github.com/ros2/rcl/blob/rolling/rcl/src/rcl/type_description_conversions.c

This provides a means to convert between the rosidl_runtime_cpp type description structs, and their corresponding type_description_interfaces messages.

Needed to support the message introspection of:

• https://github.com/ros2/rclcpp/pull/2176

Tests included. This also takes and passes along allocators.

[methylDragon]

• Linux
• Linux-aarch64
• Linux-rhel
• Windows