[cmake] urdf_LIBRARIES is still wrong

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