Pass the body to GetResult rather than the whole operation

Currently, OperationBase.ExtractData() is used to get the body of the entire operation and pass it to GetResult/GetReplicaResult for parsing. These classes then skip to the body offset.

This will make implementing decompression more difficult since decompression only affects the body and not the header. Instead, we should change ExtractData to ExtractBody and remove the header before passing to GetResult/GetReplicaResult.