Add a helper to get canonical code from status
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index 12eb651..638aa1c 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -858,6 +858,7 @@
include/grpc++/impl/codegen/service_type.h \
include/grpc++/impl/codegen/status.h \
include/grpc++/impl/codegen/status_code_enum.h \
+include/grpc++/impl/codegen/status_helper.h \
include/grpc++/impl/codegen/string_ref.h \
include/grpc++/impl/codegen/stub_options.h \
include/grpc++/impl/codegen/sync.h \