Qualcomm AI Engine Direct - Verify Windows MSVC Build in External CI

[zhaoxul-qti]

Summary

This PR adds a CI job that builds the QNN backend on Windows with MSVC (x86-64 host + ARM64 cross-compile for Windows-on-Snapdragon)

Test plan

Passing qnn-windows-msvc.yml

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/20802

• 📄 Preview Python docs built from this PR

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❌ 1 New Failure, 2 Cancelled Jobs, 1 Unrelated Failure, 2 Unclassified Failures

As of commit 8ae161f with merge base 477d278 ():

NEW FAILURE - The following job has failed:

• Lint / lintrunner (gh)
  >>> Lint for backends/qualcomm/runtime/backends/QnnBackendUnifiedRegistry.cpp:

UNCLASSIFIED FAILURES - DrCI could not classify the following jobs because the workflow did not run on the merge base. The failures may be pre-existing on trunk or introduced by this PR:

• Test QNN Backend (Windows MSVC build) / build-qnn-windows-msvc / windows-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  Process completed with exit code 1.
• trunk / test-static-llama-qnn-eval-linux (baseline, 62) / linux-job (gh) (this job did not run on the merge base, so DrCI cannot tell whether the failure is pre-existing)
  RuntimeError: Command docker exec -t 44156a840fb220282c6ba6bf73796565b8242a1c633e2f43b5712b291a60a7dd /exec failed with exit code 1

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / unittest-editable / linux / linux-job (gh)
• pull / unittest-nxp-neutron / linux-job (gh)
  ##[error]The operation was canceled.

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• pull / android / build-android (gh) (trunk failure)
  ImportError: /opt/hostedtoolcache/Python/3.11.15/x64/lib/python3.11/site-packages/executorch/extension/training/pybindings/_training_lib.cpython-311-x86_64-linux-gnu.so: undefined symbol: _ZN3c104impl3cow23materialize_cow_storageERNS_11StorageImplE

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[psiddh]

@zhaoxul-qti can you fix the linter please