[bindings] Migrate V8TestingScope out of V8Binding.h/cpp

Source/bindings/core/v8/v8.gypi

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
     'includes': [
         'custom/custom.gypi',
         '../../modules/v8/generated.gypi',
     ],
     'variables': {
@@ skipping 181 matching lines @@
         ],
         'bindings_core_v8_unittest_files': [
             'ScriptPromisePropertyTest.cpp',
             'ScriptPromiseResolverTest.cpp',
             'ScriptPromiseTest.cpp',
             'ScriptStreamerTest.cpp',
             'SerializedScriptValueTest.cpp',
             'ToV8Test.cpp',
             'V8BindingTest.cpp',
             'V8ScriptRunnerTest.cpp',
+            'V8TestingScope.cpp',
+            'V8TestingScope.h',
         ],
     },
 }