bpo-45316: Move _PyArg_Fini() to internal C API (GH-31580)

Move the private unexported _PyArg_Fini() function to the internal C
API: to the pycore_pylifecycle.h header file.

Python/getargs.c

@@ -3,6 +3,7 @@
 
 #include "Python.h"
 #include "pycore_tuple.h"         // _PyTuple_ITEMS()
+#include "pycore_pylifecycle.h"   // _PyArg_Fini
 
 #include <ctype.h>
 #include <float.h>

Python/pylifecycle.c

@@ -829,7 +829,7 @@ pycore_interp_init(PyThreadState *tstate)
     // Intern strings in deep-frozen modules first so that others
     // can use it instead of creating a heap allocated string.
     _Py_Deepfreeze_Init();
-    
+
     status = pycore_init_types(interp);
     if (_PyStatus_EXCEPTION(status)) {
         goto done;