Move balsa_fuzz_util to a separate quiche_fuzz_support glob.

While rolling QUICHE to Chromium (https://chromium-review.googlesource.com/c/chromium/src/+/7305931), if quiche_test_support depends on fuzztest (which is needed because quiche_test_support now builds balsa_fuzz_util.*), it throws the following error:

```
lld-link: error: duplicate symbol: LLVMFuzzerCustomMutator
>>> defined at obj/content/test/fuzzer/first_party_set_parser_json_fuzzer/first_party_set_parser_json_fuzzer.obj
>>> defined at obj/third_party/fuzztest/fuzztest/compatibility_mode.obj
```

This change separates balsa_fuzz_util.* to a new filelist so that we can build it separately and add the fuzztest dependency just where it is needed, to avoid having the fuzztest dependency for all of quiche_test_support.

PiperOrigin-RevId: 848182347

build/source_list.bzl

diff --git a/build/source_list.bzl b/build/source_list.bzl
index 1228670..88d0861 100644
--- a/build/source_list.bzl
+++ b/build/source_list.bzl
@@ -777,8 +777,13 @@
     "quic/tools/simple_ticket_crypter.cc",
     "quic/tools/web_transport_only_backend.cc",
 ]
-quiche_test_support_hdrs = [
+quiche_fuzz_support_hdrs = [
     "balsa/balsa_fuzz_util.h",
+]
+quiche_fuzz_support_srcs = [
+    "balsa/balsa_fuzz_util.cc",
+]
+quiche_test_support_hdrs = [
     "common/platform/api/quiche_expect_bug.h",
     "common/platform/api/quiche_fuzztest.h",
     "common/platform/api/quiche_test.h",
@@ -891,7 +896,6 @@
     "web_transport/test_tools/mock_web_transport.h",
 ]
 quiche_test_support_srcs = [
-    "balsa/balsa_fuzz_util.cc",
     "common/platform/api/quiche_test_loopback.cc",
     "common/test_tools/quiche_test_utils.cc",
     "http2/adapter/recording_http2_visitor.cc",

build/source_list.gni

diff --git a/build/source_list.gni b/build/source_list.gni
index 841dfc8..1ca3b89 100644
--- a/build/source_list.gni
+++ b/build/source_list.gni
@@ -777,8 +777,13 @@
     "src/quiche/quic/tools/simple_ticket_crypter.cc",
     "src/quiche/quic/tools/web_transport_only_backend.cc",
 ]
-quiche_test_support_hdrs = [
+quiche_fuzz_support_hdrs = [
     "src/quiche/balsa/balsa_fuzz_util.h",
+]
+quiche_fuzz_support_srcs = [
+    "src/quiche/balsa/balsa_fuzz_util.cc",
+]
+quiche_test_support_hdrs = [
     "src/quiche/common/platform/api/quiche_expect_bug.h",
     "src/quiche/common/platform/api/quiche_fuzztest.h",
     "src/quiche/common/platform/api/quiche_test.h",
@@ -891,7 +896,6 @@
     "src/quiche/web_transport/test_tools/mock_web_transport.h",
 ]
 quiche_test_support_srcs = [
-    "src/quiche/balsa/balsa_fuzz_util.cc",
     "src/quiche/common/platform/api/quiche_test_loopback.cc",
     "src/quiche/common/test_tools/quiche_test_utils.cc",
     "src/quiche/http2/adapter/recording_http2_visitor.cc",

build/source_list.json

diff --git a/build/source_list.json b/build/source_list.json
index c25053b..1f8c1a7 100644
--- a/build/source_list.json
+++ b/build/source_list.json
@@ -776,8 +776,13 @@
     "quiche/quic/tools/simple_ticket_crypter.cc",
     "quiche/quic/tools/web_transport_only_backend.cc"
   ],
+  "quiche_fuzz_support_hdrs": [
+    "quiche/balsa/balsa_fuzz_util.h"
+  ],
+  "quiche_fuzz_support_srcs": [
+    "quiche/balsa/balsa_fuzz_util.cc"
+  ],
   "quiche_test_support_hdrs": [
-    "quiche/balsa/balsa_fuzz_util.h",
     "quiche/common/platform/api/quiche_expect_bug.h",
     "quiche/common/platform/api/quiche_fuzztest.h",
     "quiche/common/platform/api/quiche_test.h",
@@ -890,7 +895,6 @@
     "quiche/web_transport/test_tools/mock_web_transport.h"
   ],
   "quiche_test_support_srcs": [
-    "quiche/balsa/balsa_fuzz_util.cc",
     "quiche/common/platform/api/quiche_test_loopback.cc",
     "quiche/common/test_tools/quiche_test_utils.cc",
     "quiche/http2/adapter/recording_http2_visitor.cc",