Add a helper to get canonical code from status

BUILD

CMakeLists.txt

Makefile

build.yaml

include/grpc++/impl/codegen/call.h

include/grpc++/impl/codegen/status_helper.h

tools/doxygen/Doxyfile.c++

tools/doxygen/Doxyfile.c++.internal

tools/run_tests/sources_and_headers.json

vsprojects/vcxproj/grpc++/grpc++.vcxproj

vsprojects/vcxproj/grpc++/grpc++.vcxproj.filters

...jects/vcxproj/grpc++_reflection/grpc++_reflection.vcxproj

...xproj/grpc++_reflection/grpc++_reflection.vcxproj.filters

vsprojects/vcxproj/grpc++_test_util/grpc++_test_util.vcxproj

...vcxproj/grpc++_test_util/grpc++_test_util.vcxproj.filters

vsprojects/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj

...s/vcxproj/grpc++_unsecure/grpc++_unsecure.vcxproj.filters

.../vcxproj/test/codegen_test_full/codegen_test_full.vcxproj

.../test/codegen_test_full/codegen_test_full.vcxproj.filters

...oj/test/codegen_test_minimal/codegen_test_minimal.vcxproj