Lift generic functionality from QuicDataReader/QuicDataWriter into Quiche The QUIC-specific functions stay in QuicDataReader/QuicDataWriter. Generally useful functions are moved into QuicheDataReader/QuicheDataWriter. gfe-relnote: n/a, no functional change PiperOrigin-RevId: 288584295 Change-Id: I53b102f56f43019a89db0aa624898ed44bb6ec11