Add aten::_nested_from_padded

[min-jean-cho]

• _nested_from_padded

[min-jean-cho]

Hi @daisyden, could you please help port the following UTs to torch-xpu-ops? Thanks!
test_nested_tensor_from_padded: https://github.com/pytorch/pytorch/blob/main/test/test_nestedtensor.py#L2961-L2975
test_nested_tensor_from_padded_fused: https://github.com/pytorch/pytorch/blob/main/test/test_nestedtensor.py#L2977-L2991

[fengyuan14]

Please fix the mixing naming. In PyTorch, usually, we have launch_xxx_kernel.

[min-jean-cho]

Thanks, updated.

[fengyuan14]

I remember we have not upstreamed DispatchKey::NestedTensorXPU. It should not work.

[min-jean-cho]

@fengyuan14 , I created #1141 to keep track of PRs related to NestedTensor support for xpu.

[fengyuan14]

I think we can leave Nested Tensor related operators for now,

1. I asked workload team people, there is no usage of Nested Tensor operators in real popular workloads.
2. We need a full plan to support Nested Tensor, like 1) we need upstream the dispatch key first. 2) Implement ~80 operators. 3) New test suite to support.
3. Why does IPEX have the operators. It's an internal requirement to align op coverage with HPU.

According to the time line, it is a bit tight for us to catch up 2.6, if we need upstream the dispatch key. We can treat it as an entire feature to support Nested Tensor in 2.7.

@EikanWang Please comment and decide.

[min-jean-cho]

Depends on #1140, #1142.