message: Include <algorithm> in .pb_text.cc generated files
  The generated code depends on this header for `std::stable_sort()`. Until now we've been lucky that this header is included indirectly on the platforms for which we build. Fixes
diff: @@ -803,6 +803,9 @@ void Generator::Generate(const FileDescriptor& fd) {
  // Add header to cc file.
  SetOutput(&cc_);
  Print("// GENERATED FILE - DO NOT MODIFY");
  + Print();
  + Print("#include <algorithm>"); // for `std::stable_sort()`
  + Print();
  headers = {GetProtoTextHeaderName(fd, true /* impl */)};
  AddHeadersToCurrentSection(headers);
  Print();
  