AsyncOperation Asynchronous unload request for an AssetBundle.
卸载捆绑包中的资源。
When unloadAllLoadedObjects is false, compressed file data for assets inside the bundle will be unloaded, but any actual objects already loaded
from this bundle will be kept intact. After calling UnloadAsync on an AssetBundle, you cannot load any more objects from that bundle and other operations on the bundle will throw InvalidOperationException.
当 unloadAllLoadedObjects 为 true 时，也将销毁从该捆绑包加载的所有对象。如果场景中有 GameObjects 引用这些资源，则对它们的引用将丢失。