gh-99113: Add Py_MOD_PER_INTERPRETER_GIL_SUPPORTED (gh-104205)

Here we are doing no more than adding the value for Py_mod_multiple_interpreters and using it for stdlib modules.  We will start checking for it in gh-104206 (once PyInterpreterState.ceval.own_gil is added in gh-104204).

Modules/_xxsubinterpretersmodule.c

@@ -822,6 +822,7 @@ error:
 
 static struct PyModuleDef_Slot module_slots[] = {
     {Py_mod_exec, module_exec},
+    {Py_mod_multiple_interpreters, Py_MOD_PER_INTERPRETER_GIL_SUPPORTED},
     {0, NULL},
 };