Enable use of ign gazebo -s on Windows (take two)

[traversaro]

New version of #1574 after the DCO errors.

🎉 New feature

This PR enable the use of ign gazebo -s on Windows. Similarly to what is done in macOS, as ign gazebo and ign gazebo -g are not supported, those options are explicitly disabled to give a nice error to the users.

Summary

Summary of changes:

• Add src/cmd directory also on Windows
• Correctly mark export visibility in ign.hh and ModelCommandAPI.hh
• Ensure that the correct directory if used in cmdgazebo.rb.in to load the gazebo plugin
• Fix the logic to copy the unversion versions of the plugins
• Fix UNIT_ign_TEST to work correctly on Windows
• Disable generation of test-only ruby scripts for ign-tools when using multiple config CMake generators, and consequently disable UNIT_ign_TEST and UNIT_ModelCommandAPI_TEST` when using multiple config CMake generators.
• As only ign gazebo -s is working, explicitly disable ign gazebo -g and ign gazebo as done on macOS .

Test it

Note, the following instructions are not complete as a version of libignition-common4 with gazebosim/gz-common#389 needs to be released before the tests work again.

Personally, I tested it with conda-forge provided depedencies. I created an environment with:

mamba create -n igngaz vs2019_win-64 cmake ninja pkg-config libignition-cmake2 libsdformat12 libignition-plugin1 libignition-transport11 libignition-msgs8 libignition-common4 libignition-fuel-tools7 libignition-gui6 libignition-physics5 libignition-sensors6 libignition-rendering6 libignition-math6 libignition-tools1 libprotobuf qt-main tinyxml2

Then, I compiled ign-gazebo with:

mamba activate igngaz
git clone https://github.com/traversaro/ign-gazebo
cd ign-gazebo
git checkout fixigngazebowinserver
mkdir build
cd build
cmake -GNinja -DCMAKE_INSTALL_PREFIX=%CONDA_PREFIX%\Library-DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_SYSTEM_RUNTIME_LIBS_SKIP:BOOL=ON ..
ninja install

After that, I was able to run correctly the server:

mamba activate igngaz
ign gazebo --verbose -s shapes.sdf

To verify the server was running correctly, I run in another terminal:

(igngaz) C:\Users\STraversaro>ign model --list

Requesting state for world [shapes]...

Available models:
    - ground_plane
    - box
    - cylinder
    - sphere
    - capsule
    - ellipsoid

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[nkoenig]

This works for me, thanks @traversaro

[nkoenig]

The failing tests look unrelated. I'll wait until CI finishes just to be sure.

[traversaro]

I am not completly sure the CI failures are unrelated, as for example INTEGRATION_thruster seems to fail on all the tests, while before this PR this was not the case. Furthermore, failure on the Ubuntu CI was also what blocked #1574 back in time. Anyhow, at this point we can try to fix the problem(s) directly on ign-gazebo6.