Create a test harness for QUIC integration tests using a simulator

This factors out some code from QuicTransportIntegrationTest that could be reused in other similar tests.

PiperOrigin-RevId: 459567821

build/source_list.json

diff --git a/build/source_list.json b/build/source_list.json
index b6386c2..f3ebe33 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -821,6 +821,7 @@
     "quiche/quic/test_tools/simulator/quic_endpoint_base.h",
     "quiche/quic/test_tools/simulator/simulator.h",
     "quiche/quic/test_tools/simulator/switch.h",
+    "quiche/quic/test_tools/simulator/test_harness.h",
     "quiche/quic/test_tools/simulator/traffic_policer.h",
     "quiche/quic/test_tools/test_certificates.h",
     "quiche/quic/test_tools/test_ticket_crypter.h",
@@ -915,6 +916,7 @@
     "quiche/quic/test_tools/simulator/quic_endpoint_base.cc",
     "quiche/quic/test_tools/simulator/simulator.cc",
     "quiche/quic/test_tools/simulator/switch.cc",
+    "quiche/quic/test_tools/simulator/test_harness.cc",
     "quiche/quic/test_tools/simulator/traffic_policer.cc",
     "quiche/quic/test_tools/test_certificates.cc",
     "quiche/quic/test_tools/test_ticket_crypter.cc",