In quic, stop blackhole detection if timer based loss detection removes all packets from in flight but no retransmission can be sent (e.g., write blocked, message frame, etc). protected by existing gfe2_reloadable_flag_quic_default_enable_5rto_blackhole_detection2.

Also add QUIC_BUGs to make sure there are bytes in flight when arming blackhole detection and when the blackhole is detected.

PiperOrigin-RevId: 315728450
Change-Id: I017bc77a95b88da460676de21cc40199d4b129c8