ackhandler: implement timer logic for path probe packets (#4940)

* remove unused bool return value from sentPacketHandler.getPTOTimeAndSpace

* ackhandler: implement timer logic for path probing packets

Path probe packets are treated differently from regular packets: The new
path might have a vastly different RTT than the original path.

Path probe packets are declared lost 1s after they are sent. This value
can be reduced, once implement proper retransmission logic for lost path
probes.

* ackhandler: declare path probes lost on OnLossDetectionTimeout

qlog/types_test.go

@@ -94,6 +94,7 @@ func TestTimerTypeStringRepresentation(t *testing.T) {
 	}{
 		{logging.TimerTypeACK, "ack"},
 		{logging.TimerTypePTO, "pto"},
+		{logging.TimerTypePathProbe, "path_probe"},
 	}
 
 	for _, tc := range testCases {