[cmake] urdf_LIBRARIES is still wrong

[JackBoosY]

When the user uses multiple configurations (dbg/rel/rel_with_dbg), urdf_LIBRARIES should be a cmake expression containing these configuration information, but at this time, using one find_library can only search for a configured library.

Suggetsions:

set(urdf_LIBRARIES urdfdom::urdfdom_model urdfdom::urdfdom_world urdfdom::urdfdom_sensor urdfdom::urdfdom_model_state)

[traversaro]

There is already a variable called urdfdom_TARGETS (see https://github.com/conda-forge/urdfdom-feedstock/blob/4f5f046cb6f8c02d90e901356d17dc1052eb7e8c/recipe/test/CMakeLists.txt#L9 for an example of its use), I guess that one can be used by downstream libraries to link all the targets exported by urdfdom.

[JackBoosY]

@traversaro Yeah, that should work. But it's just a workaround, not a fix.