Prevent directories from being backed up by iOS iCloud sandbox

UnityEngine.iOS.Device.SetNoBackupFlag(path);

For example, when the game is running, download resources or decompress resources to PersistantDataPath. If backup is not blocked, there are several impacts
. 1. It may not pass the review
. 2. Generally, the iCloud space is only 5G, so users should not want to be occupied.