Look up anFPreloadableFileinstance registered for the given FileName, and return anFArchivefrom it. If found, removes the registration so no future call to TryTakeArchive can sue the sameFArchive. If the instance is in PreloadHandle mode, the Lower-LevelFArchivewill be detached from theFPreloadableFileand returned using DetachLowerLevel. If the instance is in PreloadBytes mode, a ProxyArchive will be returned that forwards call to theFPreloadableFileinstance.