[WebGPU plugin EP] Add Win ARM64 Python package

[edgchen1]

Description

• Add WebGPU plugin EP Windows ARM64 Python package build and test
• Disable unit test building in packaging pipeline to reduce build time

Motivation and Context

Add Windows ARM64 Python package.

[Copilot]

Pull request overview

Adds Windows ARM64 support to the WebGPU plugin EP Python wheel build/test in CI, and reduces packaging build time by disabling ORT unit test builds for plugin packaging jobs.

Changes:

• Build and test the WebGPU plugin EP Python wheel on Windows ARM64 agents, producing correctly tagged win_arm64 wheels.
• Update Windows WebGPU test stage to select an ARM64 agent pool when testing ARM64 artifacts.
• Disable onnxruntime_BUILD_UNIT_TESTS in WebGPU plugin packaging builds (Linux/macOS/Windows) to reduce CI build time.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
tools/ci_build/github/linux/build_webgpu_plugin_package.sh	Disables unit test builds when building the WebGPU plugin inside Docker.
tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-test-stage.yml	Adds ARM64 pool selection and runs Python wheel tests on ARM64 hosts; switches script steps to powershell:.
tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-stage.yml	Builds Python wheels on a host matching the target arch (x64/arm64) and disables unit test builds.
tools/ci_build/github/azure-pipelines/stages/plugin-mac-webgpu-stage.yml	Disables unit test builds for the macOS ARM64 WebGPU plugin build.
tools/ci_build/github/azure-pipelines/plugin-webgpu-test-pipeline.yml	Adds a toggle to run Windows ARM64 tests and enables them by default.

Comments suppressed due to low confidence (4)

tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-test-stage.yml:47

• The PowerShell scripts no longer set $ErrorActionPreference = 'Stop'. Without this, non-terminating cmdlet errors (e.g., from Get-ChildItem/Copy-Item) can be swallowed and the job may continue in a partially-failed state. Add $ErrorActionPreference = 'Stop' at the top of this script block (and the other PowerShell blocks in this file) to keep failure behavior consistent with other pipeline stages.

This issue also appears in the following locations of the same file:

• line 92
• line 134
• line 142

    - powershell: |
        echo "creating test_venv"
        python -m venv "$(Build.BinariesDirectory)\test_venv"

        echo "activating test_venv"
        & "$(Build.BinariesDirectory)\test_venv\Scripts\Activate.ps1"

tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-test-stage.yml:100

• This PowerShell block should set $ErrorActionPreference = 'Stop' to ensure cmdlet failures (e.g., missing artifacts, Copy-Item issues) fail the job immediately. Other plugin test stages in this repo consistently set this to avoid non-terminating errors being ignored.

      - powershell: |
          $localFeedDir = "$(Build.BinariesDirectory)\local_feed"
          New-Item -ItemType Directory -Path $localFeedDir -Force | Out-Null

          # Locate the .nupkg.
          $nupkg = Get-ChildItem "$(Pipeline.Workspace)\build\webgpu_plugin_nuget\Microsoft.ML.OnnxRuntime.EP.WebGpu.*.nupkg" |
                   Select-Object -First 1
          if (-not $nupkg) {
              throw "No matching .nupkg found under $(Pipeline.Workspace)\build\webgpu_plugin_nuget"

tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-test-stage.yml:139

• Consider adding $ErrorActionPreference = 'Stop' at the start of this PowerShell script block. With the move from pwsh to powershell, cmdlet errors can become non-terminating by default, which can lead to hard-to-diagnose pipeline flakiness.

      - powershell: |
          dotnet build `
            "$(WebGpuTestProject)" `
            --configuration Release `
            -p:OrtWebGpuPackageVersion=$(OrtWebGpuPackageVersion) `
            -p:OrtCoreTestVersion=$(OrtCoreTestVersion)

tools/ci_build/github/azure-pipelines/stages/plugin-win-webgpu-test-stage.yml:147

• This PowerShell block should set $ErrorActionPreference = 'Stop' to ensure dotnet run/cmdlet failures stop the job reliably (especially after switching away from pwsh blocks that explicitly set it).

      - powershell: |
          dotnet run `
            --project "$(WebGpuTestProject)" `
            --configuration Release `
            --no-build
        displayName: 'Run NuGet package test'

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