bpo-43916: PyStdPrinter_Type uses Py_TPFLAGS_DISALLOW_INSTANTIATION (GH-25749)

The PyStdPrinter_Type type now uses the
Py_TPFLAGS_DISALLOW_INSTANTIATION flag to disallow instantiation,
rather than seting a tp_init method which always fail.

Write also unit tests for PyStdPrinter_Type.
3 files changed