Fixup recent changes to threading concerns

ResourceLoader:
- Fix invalid tokens being returned.
- Remove no longer written `ThreadLoadTask::dependent_path` and the code reading from it.
- Clear deadlock hazard by keeping the mutex unlocked during userland polling.

WorkerThreadPool:
- Include thread call queue override in the thread state reset set, which allows to simplify the code that handled that (imperfectly) in the ResourceLoader.
- Handle the mutex type correctly on entering an allowance zone.

CommandQueueMT:
- Handle the additional possibility of command buffer reallocation that mutex unlock allowance introduces.

core/object/worker_thread_pool.cpp

@@ -59,8 +59,9 @@ void WorkerThreadPool::_process_task(Task *p_task) {
 	CallQueue *call_queue_backup = MessageQueue::get_singleton() != MessageQueue::get_main_singleton() ? MessageQueue::get_singleton() : nullptr;
 
 	{
-		// Tasks must start with this unset. They are free to set-and-forget otherwise.
+		// Tasks must start with these at default values. They are free to set-and-forget otherwise.
 		set_current_thread_safe_for_nodes(false);
+		MessageQueue::set_thread_singleton_override(nullptr);
 		// Since the WorkerThreadPool is started before the script server,
 		// its pre-created threads can't have ScriptServer::thread_enter() called on them early.
 		// Therefore, we do it late at the first opportunity, so in case the task
@@ -671,7 +672,7 @@ uint32_t WorkerThreadPool::thread_enter_unlock_allowance_zone(BinaryMutex *p_mut
 
 uint32_t WorkerThreadPool::_thread_enter_unlock_allowance_zone(void *p_mutex, bool p_is_binary) {
 	for (uint32_t i = 0; i < MAX_UNLOCKABLE_MUTEXES; i++) {
-		if (unlikely(unlockable_mutexes[i] == (uintptr_t)p_mutex)) {
+		if (unlikely((unlockable_mutexes[i] & ~1) == (uintptr_t)p_mutex)) {
 			// Already registered in the current thread.
 			return UINT32_MAX;
 		}