Python: Improve the type hinting with .pyi files

Since the approval of PEP-484 many modules have been providing stub files to provide more information about all the components of the module itself.

In the case of PySide2, once the installation is done, you can find pyi files inside the module directory.
Many IDEs currently support both the PEP and the* pyi* files provided by any module, so it could be really nice if QtCreator uses them too, so the Python development workflow is improved.