Switch VGF backend from custom vulkan-headers-1.4.343 to standardized khronos (#19031)

[ocvh]

Summary:

Migrate the VGF backend's Vulkan dependencies from the custom third-party/vulkan-headers-1.4.343 package to the standardized third-party/khronos and third-party/volk packages. The custom package had a regenerated volk with ARM tensor extensions, but the standard volk and khronos 1.4.341 headers already include these extensions (VK_ARM_tensors).

Changes:

• targets.bzl: Replace custom vulkan-headers-1.4.343 deps with third-party/volk:volk_src, third-party/volk:volk-header, and third-party/khronos:vulkan-headers
• VGFBackend.cpp, VGFSetup.h: Include <volk.h> directly instead of going through the vk_api.h shim (which just forwarded to volk.h when USE_VULKAN_VOLK is defined)
• third-party/volk/BUCK: Add volk_src export_file target for direct compilation into consumer targets

Differential Revision: D100706182

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19031

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❌ 3 New Failures, 3 Unrelated Failures

As of commit 6a2e535 with merge base 1d37abd ():

NEW FAILURES - The following jobs have failed:

• Lint / lintrunner (gh)
  >>> Lint for backends/arm/runtime/VGFSetup.h:
• pull / unittest-editable / macos / macos-job (gh)
  backends/xnnpack/test/recipes/test_xnnpack_recipes.py::TestXnnpackRecipes::test_all_models_with_recipes
• trunk / test-qnn-optimum-model (fp32, roberta) / linux-job (gh)
  RuntimeError: Command docker exec -t f1386ccfe6966329d3e1ce08dcfd8cba2b69b94ef56753accb70fc710b00d9a4 /exec failed with exit code 92

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

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

• pull / unittest / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / unittest-release / windows / windows-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[meta-codesync]

@ocvh has exported this pull request. If you are a Meta employee, you can view the originating Diff in D100706182.

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