Deprecate io.OpenWrapper and _pyio.OpenWrapper: use io.open and _pyio.open
instead. Until Python 3.9, _pyio.open was not a static method and
builtins.open was set to OpenWrapper to not become a bound method when set
to a class variable. _io.open is a built-in function whereas _pyio.open is a
Python function. In Python 3.10, _pyio.open() is now a static method, and
builtins.open() is now io.open().
