ROS2 (H&J) flatland_viz not compatible

[avidbots-cameron]

Flatland_viz cannot be compiled in ROS2 Humble or Jazzy.

Many changes to the inner-workings of RViz2 components need to be brought in to the visualization package. Some work was done to start bringing flatland_viz into alignment with ROS2, but the work was never completed and the package was left with a COLCON_IGNORE file to skip its compilation.

Looking at some of the other rviz apps (outside of flatland), it may be easier to overhaul it for ROS2 using existing apps as a template rather than shoehorning in some of the required abstractions/models/interfaces, but it's not clear yet which approach is preferred.