Allow QUIC Key Update on first received 1-RTT packet

As per the specification, the first key update is allowed even if we haven't decrypted any packets: <<An endpoint MUST NOT initiate a key update prior to having confirmed the handshake (Section 4.1.2). An endpoint MUST NOT initiate a subsequent key update unless it has received an acknowledgment for a packet that was sent protected with keys from the current key phase.>> This issue was found during the IETF 110 hackathon, as another implementation was performing a key update immediately post handshake.

Protected by FLAGS_quic_reloadable_flag_quic_fix_key_update_on_first_packet.

PiperOrigin-RevId: 360781943
Change-Id: I678cd85ffdd4d014184fa6db86e8c42c64c421cd