bpo-44032: Move data stack to thread from FrameObject. (GH-26076)

* Remove 'zombie' frames. We won't need them once we are allocating fixed-size frames.

* Add co_nlocalplus field to code object to avoid recomputing size of locals + frees + cells.

* Move locals, cells and freevars out of frame object into separate memory buffer.

* Use per-threadstate allocated memory chunks for local variables.

* Move globals and builtins from frame object to per-thread stack.

* Move (slow) locals frame object to per-thread stack.

* Move internal frame functions to internal header.

Include/internal/pycore_frame.h

@@ -0,0 +1,38 @@
+#ifndef Py_INTERNAL_FRAME_H
+#define Py_INTERNAL_FRAME_H
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+enum {
+    FRAME_SPECIALS_GLOBALS_OFFSET = 0,
+    FRAME_SPECIALS_BUILTINS_OFFSET = 1,
+    FRAME_SPECIALS_LOCALS_OFFSET = 2,
+    FRAME_SPECIALS_SIZE = 3
+};
+
+static inline PyObject **
+_PyFrame_Specials(PyFrameObject *f) {
+    return &f->f_valuestack[-FRAME_SPECIALS_SIZE];
+}
+
+/* Returns a *borrowed* reference. */
+static inline PyObject *
+_PyFrame_GetGlobals(PyFrameObject *f)
+{
+    return _PyFrame_Specials(f)[FRAME_SPECIALS_GLOBALS_OFFSET];
+}
+
+/* Returns a *borrowed* reference. */
+static inline PyObject *
+_PyFrame_GetBuiltins(PyFrameObject *f)
+{
+    return _PyFrame_Specials(f)[FRAME_SPECIALS_BUILTINS_OFFSET];
+}
+
+int _PyFrame_TakeLocals(PyFrameObject *f);
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERNAL_FRAME_H */