sched: add helper functions for opening and resolving handles for a task

sched/thread.c

@@ -17,6 +17,11 @@ kern_status_t thread_object_type_init(void)
 	return object_type_register(&thread_type);
 }
 
+struct thread *thread_cast(struct object *obj)
+{
+	return THREAD_CAST(obj);
+}
+
 struct thread *thread_alloc(void)
 {
 	struct object *thread_obj = object_create(&thread_type);