gh-132775: Unrevert "Add _PyCode_VerifyStateless()" (gh-133528)

This reverts commit 3c73cf5 (gh-133497), which itself reverted
the original commit d270bb5 (gh-133221).

We reverted the original change due to failing android tests.
The checks in _PyCode_CheckNoInternalState() were too strict,
so we've relaxed them.

Include/internal/pycore_code.h

@@ -614,6 +614,47 @@ PyAPI_FUNC(int) _PyCode_SetUnboundVarCounts(
         PyObject *globalsns,
         PyObject *builtinsns);
 
+
+/* "Stateless" code is a function or code object which does not rely on
+ * external state or internal state.  It may rely on arguments and
+ * builtins, but not globals or a closure.  Thus it does not rely
+ * on __globals__ or __closure__, and a stateless function
+ * is equivalent to its code object.
+ *
+ * Stateless code also does not keep any persistent state
+ * of its own, so it can't have any executors, monitoring,
+ * instrumentation, or "extras" (i.e. co_extra).
+ *
+ * Stateless code may create nested functions, including closures.
+ * However, nested functions must themselves be stateless, except they
+ * *can* close on the enclosing locals.
+ *
+ * Stateless code may return any value, including nested functions and closures.
+ *
+ * Stateless code that takes no arguments and doesn't return anything
+ * may be treated like a script.
+ *
+ * We consider stateless code to be "portable" if it does not return
+ * any object that holds a reference to any of the code's locals.  Thus
+ * generators and coroutines are not portable.  Likewise a function
+ * that returns a closure is not portable.  The concept of
+ * portability is useful in cases where the code is run
+ * in a different execution context than where
+ * the return value will be used. */
+
+PyAPI_FUNC(int) _PyCode_CheckNoInternalState(PyCodeObject *, const char **);
+PyAPI_FUNC(int) _PyCode_CheckNoExternalState(
+        PyCodeObject *,
+        _PyCode_var_counts_t *,
+        const char **);
+PyAPI_FUNC(int) _PyCode_VerifyStateless(
+        PyThreadState *,
+        PyCodeObject *,
+        PyObject *globalnames,
+        PyObject *globalsns,
+        PyObject *builtinsns);
+
+PyAPI_FUNC(int) _PyCode_CheckPureFunction(PyCodeObject *, const char **);
 PyAPI_FUNC(int) _PyCode_ReturnsOnlyNone(PyCodeObject *);