bpo-36929: Modify io/re tests to allow for missing mod name (#13392)

* bpo-36929: Modify io/re tests to allow for missing mod name

For a vanishingly small number of internal types, CPython sets the
tp_name slot to mod_name.type_name, either in the PyTypeObject or the
PyType_Spec. There are a few minor places where this surfaces:

* Custom repr functions for those types (some of which ignore the
  tp_name in favor of using a string literal, such as _io.TextIOWrapper)
* Pickling error messages

The test suite only tests the former. This commit modifies the test
suite to allow Python implementations to omit the module prefix.

https://bugs.python.org/issue36929