add new method, string method, spanner methods, spanner handler, and pregenerate
add new method, string method, spanner methods, spanner handler, and pregenerate

tcncloud/protoc-gen-persist,iamneal/protoc-gen-persist,iamneal/protoc-gen-persist,namtzigla/protoc-gen-persist,tcncloud/protoc-gen-persist,tcncloud/protoc-gen-persist,iamneal/protoc-gen-persist