bpo-35059: Convert PyObject_INIT() to function (GH-10077)

* Convert PyObject_INIT() and PyObject_INIT_VAR() macros to static
  inline functions.
* Fix usage of these functions: cast to PyObject* or PyVarObject*.

Objects/floatobject.c

@@ -124,7 +124,7 @@ PyFloat_FromDouble(double fval)
             return PyErr_NoMemory();
     }
     /* Inline PyObject_New */
-    (void)PyObject_INIT(op, &PyFloat_Type);
+    (void)PyObject_INIT((PyObject *)op, &PyFloat_Type);
     op->ob_fval = fval;
     return (PyObject *) op;
 }