Create ConnectUdpTunnel

Will be used by QUICHE toy server in a subsequent CL to create a CONNECT-UDP-capable backend.

PiperOrigin-RevId: 479730001

build/source_list.bzl

diff --git a/build/source_list.bzl b/build/source_list.bzl
index 62d8265..9ab0ba3 100644
--- a/build/source_list.bzl
+++ b/build/source_list.bzl
@@ -704,6 +704,7 @@
     "quic/platform/api/quic_default_proof_providers.h",
     "quic/tools/connect_server_backend.h",
     "quic/tools/connect_tunnel.h",
+    "quic/tools/connect_udp_tunnel.h",
     "quic/tools/fake_proof_verifier.h",
     "quic/tools/quic_backend_response.h",
     "quic/tools/quic_client_base.h",
@@ -727,6 +728,7 @@
     "common/platform/api/quiche_file_utils.cc",
     "quic/tools/connect_server_backend.cc",
     "quic/tools/connect_tunnel.cc",
+    "quic/tools/connect_udp_tunnel.cc",
     "quic/tools/quic_backend_response.cc",
     "quic/tools/quic_client_base.cc",
     "quic/tools/quic_memory_cache_backend.cc",
@@ -1245,6 +1247,7 @@
     "quic/test_tools/simulator/quic_endpoint_test.cc",
     "quic/test_tools/simulator/simulator_test.cc",
     "quic/tools/connect_tunnel_test.cc",
+    "quic/tools/connect_udp_tunnel_test.cc",
     "quic/tools/quic_memory_cache_backend_test.cc",
     "quic/tools/quic_tcp_like_trace_converter_test.cc",
     "quic/tools/simple_ticket_crypter_test.cc",