[TIoStatusOr](API\Runtime\Core\IO\TIoStatusOr)< [FIoMappedRegion](API\Runtime\Core\IO\FIoMappedRegion) > OpenMapped ( const [FIoChunkId](API\Runtime\Core\IO\FIoChunkId) & ChunkId, const [FIoReadOptions](API\Runtime\Core\IO\FIoReadOptions) & Options )