Break circular dependency between repositories by splitting out package

See: https://gitlab.com/micro-ROS/ros_tracing/ros2_tracing/-/issues/90#note_331281742

Otherwise, the circular dependency means that the initial release for a distro needs to be done in two steps.

The packages that would need to be split out are:

• ros2trace, since it depends on ros2cli which depends on rclpy --> rcl --> tracetools. Maybe this one could be moved to ros2cli?
• tracetools_test, since it depends on rclcpp --> tracetools. For this one, we could probably keep the trace-related test tools (TraceTestCase) in a package here and move the actual test code to another package & to another repo.
  • package split: !245 (merged)