Mojo: Unify the disparate source and header files into 3

mojo/public/bindings/generators/cpp_templates/module.cc-template

+// Copyright $YEAR The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "$HEADER"
+
+#include "mojo/public/bindings/lib/message_builder.h"
+#include "$INTERNAL_HEADER"
+
+namespace sample {
+namespace {
+
+#pragma pack(push, 1)
+#if defined(__clang__)
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wunused-private-field"
+#endif
+$PARAM_DEFINITIONS
+#if defined(__clang__)
+#pragma clang diagnostic pop
+#endif
+#pragma pack(pop)
+
+}  // namespace
+
+$STRUCT_DEFINITIONS
+
+$INTERFACE_DEFINITIONS
+}  // namespace sample
+
+namespace mojo {
+namespace internal {
+
+$STRUCT_SERIALIZATION_DEFINITIONS
+
+$INTERFACE_SERIALIZATION_DEFINITIONS
+
+}  // namespace internal
+}  // namespace mojo