Allow selecting whether to use system dependencies or download vendored

[diegoferigo]

Fix #256.

Latest CMake refactoring done in #233.

[diegoferigo]

I got the following error when packaging the wheel (and not when builiding the plain CMake project):

CMake Error: install(EXPORT "ScenarioGazeboExport" ...) includes target "GazeboSimulator" which requires target "tiny-process-library" that is not in any export set.
CMake Error in cpp/scenario/gazebo/CMakeLists.txt:
export called with target "GazeboSimulator" which requires target
"tiny-process-library" that is not in any export set.

Error in CI here.

Last time I had to resort to a workaround that I tried to remove in a27723e. Apparently is still required. Trying another alternative in 9da3a7a from https://gitlab.kitware.com/cmake/cmake/-/issues/15415#note_634114.

cc @traversaro

[traversaro]

Another related issue may be https://gitlab.kitware.com/cmake/cmake/-/issues/18935 . In general OBJECT libraries and installations are definitely an area of CMake that is not really robust at the moment.

[diegoferigo]

Another related issue may be https://gitlab.kitware.com/cmake/cmake/-/issues/18935 . In general OBJECT libraries and installations are definitely an area of CMake that is not really robust at the moment.

Yep, the fix didn't solve it:

CMake Error in cpp/scenario/gazebo/CMakeLists.txt:
export called with target "GazeboSimulator" which requires target
"tiny-process-library" that is not in any export set.

[diegoferigo]

I tried with STATIC library but when packaging the wheel, the .a of TPL gets included and I don't like that. I reverted to OBJECT. In this case, a new exported target ScenarioGazebo::tiny-process-library is created but it looks harmless.

Let's wait CI and merge if this is ok.