gfe-relnote: In QUIC sent packet manager, replace handshake_confirmed_ and forward_secure_packet_acked_ with handshake_state_. No functional change expected. Not protected. Also rename QuicConnection::IsHandshakeConfirmed to QuicConnection::IsHandshakeComplete. PiperOrigin-RevId: 281069350 Change-Id: Id40366a9148add245798b1805ae5f1e3a46d5fc6