bpo-36842: Implement PEP 578 (GH-12613)

Adds sys.audit, sys.addaudithook, io.open_code, and associated C APIs.

Python/pythonrun.c

@@ -1091,6 +1091,12 @@ run_mod(mod_ty mod, PyObject *filename, PyObject *globals, PyObject *locals,
     co = PyAST_CompileObject(mod, filename, flags, -1, arena);
     if (co == NULL)
         return NULL;
+
+    if (PySys_Audit("exec", "O", co) < 0) {
+        Py_DECREF(co);
+        return NULL;
+    }
+
     v = run_eval_code_obj(co, globals, locals);
     Py_DECREF(co);
     return v;