Install library so into python module dir

We do the same a PySide and install the target library into the python
module this. This way the bindings can work without need to export
system paths.

cmake/KDAB/modules/PySide2ModuleBuild.cmake

@@ -129,6 +129,7 @@ macro(CREATE_PYTHON_BINDINGS
             PREFIX ""
             OUTPUT_NAME ${MODULE_NAME}
             LIBRARY_OUTPUT_DIRECTORY ${MODULE_OUTPUT_DIR}
+            INSTALL_RPATH "$ORIGIN"
         )
 
         if(WIN32)