Move gtest-parallel to flutter/third_party (flutter/engine#47393)

As part of eliminating the Flutter buildroot (https://github.com/flutter/flutter/issues/67373), we are moving all third-party dependencies from //third_party to //flutter/third_party.

Once all third-party dependencies have been migrated, tooling and config will be moved and the buildroot will be eliminated altogether.

No tests changed because there is no semantic change to this PR. This is simply relocating a dependency.

DEPS

@@ -294,7 +294,7 @@ deps = {
   'src/third_party/khronos':
    Var('chromium_git') + '/chromium/src/third_party/khronos.git' + '@' + '676d544d2b8f48903b7da9fceffaa534a5613978',
 
-   'src/third_party/gtest-parallel':
+   'src/flutter/third_party/gtest-parallel':
    Var('chromium_git') + '/external/github.com/google/gtest-parallel' + '@' + '38191e2733d7cbaeaef6a3f1a942ddeb38a2ad14',
 
   'src/third_party/benchmark':

engine/src/flutter/ci/licenses_golden/excluded_files

@@ -509,6 +509,13 @@
 ../../../flutter/third_party/glfw/src/CMakeLists.txt
 ../../../flutter/third_party/glfw/tests
 ../../../flutter/third_party/gn
+../../../flutter/third_party/gtest-parallel/.git
+../../../flutter/third_party/gtest-parallel/.gitignore
+../../../flutter/third_party/gtest-parallel/CONTRIBUTING.md
+../../../flutter/third_party/gtest-parallel/README.md
+../../../flutter/third_party/gtest-parallel/gtest_parallel.py
+../../../flutter/third_party/gtest-parallel/gtest_parallel_mocks.py
+../../../flutter/third_party/gtest-parallel/gtest_parallel_tests.py
 ../../../flutter/third_party/imgui
 ../../../flutter/third_party/ninja
 ../../../flutter/third_party/rapidjson/.git
@@ -2121,13 +2128,6 @@
 ../../../third_party/google_fonts_for_unit_tests
 ../../../third_party/googletest
 ../../../third_party/gradle
-../../../third_party/gtest-parallel/.git
-../../../third_party/gtest-parallel/.gitignore
-../../../third_party/gtest-parallel/CONTRIBUTING.md
-../../../third_party/gtest-parallel/README.md
-../../../third_party/gtest-parallel/gtest_parallel.py
-../../../third_party/gtest-parallel/gtest_parallel_mocks.py
-../../../third_party/gtest-parallel/gtest_parallel_tests.py
 ../../../third_party/harfbuzz/.ci/requirements.txt
 ../../../third_party/harfbuzz/.clang-format
 ../../../third_party/harfbuzz/.editorconfig

engine/src/flutter/testing/run_tests.py

@@ -211,7 +211,8 @@ def build_engine_executable_command(
     test_command = [executable] + flags
     if gtest:
       gtest_parallel = os.path.join(
-          BUILDROOT_DIR, 'third_party', 'gtest-parallel', 'gtest-parallel'
+          BUILDROOT_DIR, 'flutter', 'third_party', 'gtest-parallel',
+          'gtest-parallel'
       )
       test_command = ['python3', gtest_parallel] + test_command