Commingled install and devel workspace overlaying

[lucasw]

Using base_catkin_ws built with --install and then source base_catkin_ws/install/setup.bash, then building a devel catkin_ws seems fine, at least when no packages are actually overlaying (but expected it should still work) and only in very small overlaying workspace.

If this fully works then the debian install process that just puts all of install/ into /opt/ros/one/ is good enough.

Does overlaying install on devel work?

Thought I tried some combination that didn't work, possibly I was mistaken or packages that caused it to fail have been fixed..

[lucasw]

Given overlaying anything on base install catkin_ws works, should always do that, that will be cleaner (ROS_PACKAGE_PATH will be much shorter) and test the ability of every underlying package to do a proper install (and not miss needed files).

[lucasw]

Could make a 20.04 deb of all modified packages (and packages that aren't apt installable even in 20.04 using buildfarm) and use that in github actions, also could have several layers of packages in separate debs that will greatly shorten action build times. Or stop using the buildfarm and only use debian base packages in 20.04, this will make 20.04 and 22.04 builds much more similar.