py: Add new cstack API for stack checking, with limit margin macro.

Currently the stack limit margin is hard-coded in each port's call to
`mp_stack_set_limit()`, but on threaded ports it's fiddlier and can lead to
bugs (such as incorrect thread stack margin on esp32).

This commit provides a new API to initialise the C Stack in one function
call, with a config macro to set the margin.  Where possible the new call
is inlined to reduce code size in thread-free ports.

Intended replacement for `MP_TASK_STACK_LIMIT_MARGIN` on esp32.

The previous `stackctrl.h` API is still present and unmodified apart from a
deprecation comment.  However it's not available when the
`MICROPY_PREVIEW_VERSION_2` macro is set.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

py/runtime.c

@@ -43,7 +43,7 @@
 #include "py/stream.h"
 #include "py/runtime.h"
 #include "py/builtin.h"
-#include "py/stackctrl.h"
+#include "py/cstack.h"
 #include "py/gc.h"
 
 #if MICROPY_DEBUG_VERBOSE // print debugging info
@@ -1374,7 +1374,7 @@ mp_obj_t mp_iternext_allow_raise(mp_obj_t o_in) {
 // will always return MP_OBJ_STOP_ITERATION instead of raising StopIteration() (or any subclass thereof)
 // may raise other exceptions
 mp_obj_t mp_iternext(mp_obj_t o_in) {
-    MP_STACK_CHECK(); // enumerate, filter, map and zip can recursively call mp_iternext
+    mp_cstack_check(); // enumerate, filter, map and zip can recursively call mp_iternext
     const mp_obj_type_t *type = mp_obj_get_type(o_in);
     if (TYPE_HAS_ITERNEXT(type)) {
         MP_STATE_THREAD(stop_iteration_arg) = MP_OBJ_NULL;