gh-91320: Add _Py_reinterpret_cast() macro (#91959)

Fix C++ compiler warnings about "old-style cast"
(g++ -Wold-style-cast) in the Python C API.  Use C++
reinterpret_cast<> and static_cast<> casts when the Python C API is
used in C++.

Example of fixed warning:

    Include/object.h:107:43: error: use of old-style cast to
    ‘PyObject*’ {aka ‘struct _object*’} [-Werror=old-style-cast]
    #define _PyObject_CAST(op) ((PyObject*)(op))

Add _Py_reinterpret_cast() and _Py_static_cast() macros.