message: [XLA] Redesign: implement ReduceAll.
diff: @@ -1417,7 +1417,12 @@ XlaOp XlaBuilder::Reduce(
  XlaOp XlaBuilder::ReduceAll(const XlaOp& operand, const XlaOp& init_value,
  const XlaComputation& computation) {
  - return UnimplementedOp();
  + return NoteErrorOrReturn([&]() -> StatusOr<XlaOp> {
  + TF_ASSIGN_OR_RETURN(const Shape& operand_shape, GetShape(operand));
  + std::vector<int64> all_dimnos(ShapeUtil::Rank(operand_shape));
  + std::iota(all_dimnos.begin(), all_dimnos.end(), 0);
  + return Reduce(operand, init_value, computation, all_dimnos);
  + });
  }
  XlaOp XlaBuilder::ReduceWindow(
  