Add xkb_state_serialize functions

src/lib.rs

@@ -276,6 +276,8 @@ functions:
     fn xkb_state_key_get_level(*mut xkb_state, xkb_keycode_t, xkb_layout_index_t) -> xkb_level_index_t,
     fn xkb_state_mod_name_is_active(*mut xkb_state, *const c_char, xkb_state_component) -> c_int,
     fn xkb_state_mod_index_is_active(*mut xkb_state, xkb_mod_index_t, xkb_state_component) -> c_int,
+    fn xkb_state_serialize_mods(*mut xkb_state, xkb_state_component) -> xkb_mod_mask_t,
+    fn xkb_state_serialize_layout(*mut xkb_state, xkb_state_component) -> xkb_layout_index_t,
 );
 
 // Compose and dead-keys support module