Generate int variants for nchw_to_image and image_to_nchw (#2488)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/2488

Required for `aten.max_pool2d_with_indices` which is coming soon, where we work with an `int` tensor on Vulkan.
ghstack-source-id: 219127762
exported-using-ghexport

Reviewed By: copyrightly, SS-JIA

Differential Revision: D54961928

fbshipit-source-id: 75f0955b47b0dac4106dade561e90034a94bd785