input-method: send modifiers in set_keyboard

Otherwise the client might have an outdated modifiers state. The same is
done in wlr_seat_keyboard [1].

[1]: 8348fc3ef8/types/seat/wlr_seat_keyboard.c (L163)

types/wlr_input_method_v2.c

@@ -259,6 +259,9 @@ void wlr_input_method_keyboard_grab_v2_set_keyboard(
 			handle_keyboard_destroy;
 		wl_signal_add(&keyboard->events.destroy,
 			&keyboard_grab->keyboard_destroy);
+
+		wlr_input_method_keyboard_grab_v2_send_modifiers(keyboard_grab,
+			&keyboard->modifiers);
 	}
 
 	keyboard_grab->keyboard = keyboard;