Add CI pipeline for WebGPU EP model testing

[qjia7]

No description provided.

[Copilot]

Pull request overview

This PR adds CI pipeline infrastructure to enable WebGPU execution provider testing on Windows x64. The changes introduce a new GitHub Actions workflow and supporting test configuration files to build and test ONNX Runtime GenAI with WebGPU EP support.

Changes:

• Added GitHub Actions workflow for Windows WebGPU x64 builds with automated testing
• Introduced WebGPU-specific Python test dependencies (PyTorch CPU and onnxruntime-webgpu packages)
• Extended test utilities to support WebGPU model building with specialized options and runtime configuration

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
.github/workflows/win-webgpu-x64-build.yml	New CI workflow for building and testing WebGPU EP on Windows x64, following established patterns from other EP workflows
test/python/webgpu/torch/requirements.txt	PyTorch CPU dependencies for WebGPU model building
test/python/webgpu/ort/requirements.txt	ONNX Runtime WebGPU package dependency (dev version)
test/python/_test_utils.py	WebGPU-specific model building options and runtime configuration via genai_config.json modification
test/python/test_onnxruntime_genai.py	Integration of WebGPU model download when WebGPU EP is available