py/objtype: Allow passing keyword arguments to native base __init__.

Allowing passing keyword arguments to a native base's __init__, i.e.
`make_new` in the C code.  Previously only positional arguments were
allowed.

The main trade-off in this commit is that every call to the native base's
`make_new` is now going to be preceded by a call to
`mp_map_init_fixed_table` even though most of what that does is unused and
instead it merely serves as a way to pass the number of keyword arguments.

Fixes issue #15465.

Signed-off-by: stijn <stijn@ignitron.net>

py/objtype.c

@@ -85,14 +85,14 @@ static int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
 
 // This wrapper function allows a subclass of a native type to call the
 // __init__() method (corresponding to type->make_new) of the native type.
-static mp_obj_t native_base_init_wrapper(size_t n_args, const mp_obj_t *args) {
+static mp_obj_t native_base_init_wrapper(size_t n_args, const mp_obj_t *args, mp_map_t *kw_args) {
     mp_obj_instance_t *self = MP_OBJ_TO_PTR(args[0]);
     const mp_obj_type_t *native_base = NULL;
     instance_count_native_bases(self->base.type, &native_base);
-    self->subobj[0] = MP_OBJ_TYPE_GET_SLOT(native_base, make_new)(native_base, n_args - 1, 0, args + 1);
+    self->subobj[0] = MP_OBJ_TYPE_GET_SLOT(native_base, make_new)(native_base, n_args - 1, kw_args->used, args + 1);
     return mp_const_none;
 }
-static MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(native_base_init_wrapper_obj, 1, MP_OBJ_FUN_ARGS_MAX, native_base_init_wrapper);
+static MP_DEFINE_CONST_FUN_OBJ_KW(native_base_init_wrapper_obj, 1, native_base_init_wrapper);
 
 #if !MICROPY_CPYTHON_COMPAT
 static