[Reland] Install xpu codegen header to torch/include

[guangyey]

Motivation

This PR addresses a code generation issue related to XPU. Currently, there are two separate codegen paths for XPU:

1. Stock PyTorch – Generates code for oneDNN ops.
2. torch-xpu-ops – Generates code for SYCL kernel ops.

The corresponding build directories are:

1. build/aten/src/ATen (for stock PyTorch)
2. build/xpu/ATen (for torch-xpu-ops)

However, in the torch-xpu-ops codegen, we mistakenly omitted installing XPU op headers from build/xpu/ATen/ops to build/aten/src/ATen/ops. This PR fixes the issue and also removes some unnecessary code for better maintainability.

Solution

We copy the codegen from torch-xpu-ops to stock PyTorch

Additional Context

The original PR is #1405
Fix pytorch/pytorch#145902

[Copilot]

Pull Request Overview

This PR fixes the header installation for the torch-xpu-ops codegen by updating include paths for XPU op headers and adjusting CMake scripts.

• Updated include directives in multiple XPU source files to reference the proper directory (ATen/ops).
• Modified CMakeLists.txt and Codegen.cmake to copy generated XPU op headers into stock PyTorch’s include directory.

Reviewed Changes

Copilot reviewed 50 out of 50 changed files in this pull request and generated no comments.

File	Description
src/ATen/native/xpu/*.cpp	Updated include paths from "xpu/ATen/ops" to "ATen/ops".
src/ATen/CMakeLists.txt	Added installation of generated XPU header files into ATen/ops.
cmake/Codegen.cmake	Introduced variable BUILD_TORCH_ATEN_GENERATED and header install commands to support header installation.

[dvrogozh]

Big one, difficult to review. But it's better with this change than without as it blocks certain types of pytorch xpu usage. Better to land and face consequences, if any. I hope it won't be reverted again. If something will go wrong - please, let's discuss before doing harsh reverts!

[guangyey]

@chunhuanMeng May I know if the Windows build issue has been resolved.

[chunhuanMeng]

@chunhuanMeng May I know if the Windows build issue has been resolved.

Yes, I have tested it on Windows.

[guangyey]

Let’s try landing it and see what happens.