message: Call "Reserve" method in `ConvertXXXElementsAttr` functions which slightly improve the efficiency.
diff: @@ -264,7 +264,8 @@ void ConvertElementsAttr(const mlir::DenseElementsAttr attr,
  if (attr.isSplat()) {
  output->Add(attr.getSplatValue<T>());
  } else {
  - for (auto value : attr.getValues<T>()) output->Add(value);
  + output->Reserve(attr.getNumElements());
  + for (auto value : attr.getValues<T>()) output->AddAlreadyReserved(value);
  }
  }
  @@ -275,8 +276,9 @@ void ConvertHalfElementsAttr(const mlir::DenseElementsAttr attr,
  if (attr.isSplat()) {
  output->Add(attr.getSplatValue<Eigen::half>().x);
  } else {
  + output->Reserve(attr.getNumElements());
  for (const Eigen::half value : attr.getValues<Eigen::half>())
  - output->Add(value.x);
  + output->AddAlreadyReserved(value.x);
  }
  }
  @@ -287,7 +289,9 @@ void ConvertIntElementsAttr(const mlir::DenseIntElementsAttr attr,
  if (attr.isSplat()) {
  output->Add((*attr.begin()).getSExtValue());
  } else {
  - for (const llvm::APInt val : attr) output->Add(val.getSExtValue());
  + output->Reserve(attr.getNumElements());
  + for (const llvm::APInt val : attr)
  + output->AddAlreadyReserved(val.getSExtValue());
  }
  }
  @@ -296,8 +300,9 @@ void ConvertBfloat16ElementsAttr(const mlir::DenseElementsAttr attr,
  if (attr.isSplat()) {
  output->Add(attr.getSplatValue<bfloat16>().value);
  } else {
  + output->Reserve(attr.getNumElements());
  for (const bfloat16 value : attr.getValues<bfloat16>())
  - output->Add(value.value);
  + output->AddAlreadyReserved(value.value);
  }
  }
  