update tensor::SizesType to exec_aten::SizeType (#1988)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1988

There's no SizesType under at::Tensor, tensor::SizesType might cause issue under aten mode.
Update it to exec_aten::SizesType to fix the issue.

Reviewed By: manuelcandales

Differential Revision: D53821056

fbshipit-source-id: af63fa11bed826811f09024a27c7a8563a31bd9c