py/map: allow disabling reallocation for specific dicts

[romanz]

Also, enable this feature for __main__ and sys.modules.

[romanz]

Following trezor/trezor-firmware#4823 (comment).

[romanz]

If no_realloc is set in runtime.c, it causes CI failures (e.g. in core unittests) -> force-pushed a fix:

diff --git a/py/runtime.c b/py/runtime.c
index af360970b..696b99825 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -103,11 +103,9 @@ void mp_init(void) {
 
     // init global module dict
     mp_obj_dict_init(&MP_STATE_VM(mp_loaded_modules_dict), MICROPY_LOADED_MODULES_DICT_SIZE);
-    MP_STATE_VM(mp_loaded_modules_dict).map.no_realloc = 1;
 
     // initialise the __main__ module
     mp_obj_dict_init(&MP_STATE_VM(dict_main), MICROPY_MAIN_DICT_SIZE);
-    MP_STATE_VM(dict_main).map.no_realloc = 1;
     mp_obj_dict_store(MP_OBJ_FROM_PTR(&MP_STATE_VM(dict_main)), MP_OBJ_NEW_QSTR(MP_QSTR___name__), MP_OBJ_NEW_QSTR(MP_QSTR___main__));
 
     // locals = globals for outer module (see Objects/frameobject.c/PyFrame_New())

[romanz]

Another approach is used in trezor/trezor-firmware#4842.