Fix build errors in Ubuntu Lunar when fetched directly

[Ryanf55]

I had some build/include errors when building in Ubuntu Lunar (23.04) when compiling nav2 from source.

I've modified the CMakelists to make use of the target_sources command. The library is now a level higher. The commands to target_include_directories are properly scoped depending on the directory, especially for the generated export header. No more traversing up directories and back down.

Relates to https://github.com/ros-perception/vision_opencv/pull/419