Add full SYCL support for Windows builds

[Copilot]

Type

• New feature (non-breaking change which adds functionality)

Motivation and Context

Adds full Windows SYCL support to align with PyTorch 2025.3.1 (oneAPI 2025.3.1). Migrates the Windows CI matrix from CUDA ON/OFF to target cpu, cuda, and xpu (SYCL), enabling open3d_xpu Python wheels and C++ binary distributions with SYCL acceleration on Windows.

Checklist:

• I have run python util/check_style.py --apply to apply Open3D code style to my code.
• This PR changes Open3D behavior or adds new functionality.
  • Both C++ (Doxygen) and Python (Sphinx / Google style) documentation is updated accordingly.
  • I have added or updated C++ and / or Python unit tests OR included test results here.
• I will follow up and update the code if CI fails.

Description

CMake & Build Infrastructure

• Relaxed Platform Checks: Lifted the Linux-only restriction on BUILD_SYCL_MODULE in CMakeLists.txt to support Windows builds.
• Packaging Names: Appended -sycl to the packaged distribution name in cmake/Open3DPackaging.cmake when built with SYCL.
• XPU Python Pathing: Routed compiled SYCL bindings to open3d/xpu in cpp/pybind/CMakeLists.txt and updated cpp/pybind/make_python_package.cmake to bundle the xpu directory structure.

Python Runtime & DLL Loading

• Dynamic DLL Resolution: Configured Windows Python initialization in python/open3d/__init__.py to locate and load Intel compiler, oneMKL, and oneTBB redistributable DLL directories. Resolves the runtime directories dynamically using ONEAPI_ROOT (or default paths) with os.add_dll_directory to prevent DLL loading errors on Python 3.8+.
• Subpackage Routing: Updated visualization, ML, and ML contrib initializers to import symbols correctly from the xpu submodule when running on a SYCL-enabled (xpu) binary.

GHA Windows CI / CD Matrix

• Matrix Migration: Changed the GHA strategy matrix in .github/workflows/windows.yml from BUILD_CUDA_MODULE: [ON, OFF] to device: [cpu, cuda, xpu].
• oneAPI Silent Provisioning: Added a setup step to fetch, silently install, and verify the exit codes for oneMKL 2025.3.1.10 and the Intel Compiler 2025.3.1.15 on Windows GHA runners when targeting xpu.
• Toolchain & Linker Config: Configured CMake to invoke MSBuild with -T "Intel(R) oneAPI DPC++ Compiler" and search for OpenCL dynamically.
• Unified Wheel Tests: Configured wheel building and testing to support both CPU and XPU variants, using PowerShell pattern-matching to automatically discover and verify the built wheel.

import open3d as o3d

# Check built configuration
print("SYCL Module Compiled:", o3d._build_config["BUILD_SYCL_MODULE"])

# Verify device availability
if o3d._build_config["BUILD_SYCL_MODULE"]:
    print("SYCL Device Available:", o3d.core.sycl.is_available())

[update-docs]

Thanks for submitting this pull request! The maintainers of this repository would appreciate if you could update the CHANGELOG.md based on your changes.