Arm backend: update Vulkan SDK setup for newer glslc

[robell]

update Vulkan SDK setup for newer glslc, which fixes testing time shader compiles where the system had an old glslc (and revises the version used in our test scripts)
Also mark custom shader tests as vgf so they run in just the VGF or general testing, not in e.g. baremetal.

cc @SS-JIA @manuelcandales @digantdesai @cbilgin @freddan80 @per @zingo @oscarandersson8218 @mansnils @Sebastian-Larsson @rascani

[pytorch-bot]

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❌ 2 New Failures, 2 Unrelated Failures

As of commit da2d361 with merge base 721e641 ():

NEW FAILURES - The following jobs have failed:

• Test WebGPU Backend / test-webgpu / test-backend-linux (webgpu, models) / linux-job (gh)
  RuntimeError: Command docker exec -t 86179143e71358f653b472e79bedcb6157fd517fc866f290ee573c79db1671db /exec failed with exit code 1
• Test WebGPU Backend / test-webgpu / test-backend-linux (webgpu, operators) / linux-job (gh)
  RuntimeError: Command docker exec -t e263d395d9761c91ad9d5d32d5e5f942e3ff4a54f4da6fe403f76af0056829b8 /exec failed with exit code 1

FLAKY - The following job failed but was likely due to flakiness present on trunk:

• trunk / test-arm-backend-ethos-u (test_smaller_stories_llama_tosa) / linux-job (gh) (similar failure)
  ##[error]The operation was canceled.

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

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

• trunk / test-arm-backend-vkml (test_smaller_stories_llama_vkml) / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[Copilot]

Pull request overview

Updates the Arm VGF/Vulkan tooling and tests to rely on a newer Vulkan SDK glslc (to avoid slow shader compilation with older host glslc), and scopes custom-shader-related pytest coverage to VGF-only runs.

Changes:

• Bump referenced Vulkan SDK version to 1.4.341.1 in setup docs and Vulkan CMake error messaging.
• Update Arm Vulkan SDK setup script to download/use SDK glslc and prepend the SDK bin directory on PATH.
• Rename custom-shader-related ARM tests to include _vgf_ so they run under the VKML/VGF test selection and are excluded from baremetal flows.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
docs/source/backends/arm-vgf/tutorials/vgf-getting-started.md	Updates the Vulkan SDK version shown in the glslc PATH troubleshooting guidance.
backends/arm/scripts/docgen/vgf/vgf-getting-started-tutorial.md.in	Keeps the generated tutorial source in sync with the updated Vulkan SDK version.
backends/vulkan/cmake/ShaderLibrary.cmake	Updates the minimum Vulkan SDK version mentioned in the glslc missing error message.
backends/arm/scripts/vulkan_utils.sh	Moves to Vulkan SDK 1.4.341.1 (URLs + SHA256) and prepends SDK bin to PATH to prefer SDK glslc.
backends/arm/test/passes/test_rewrite_grid_sampler_to_tosa_custom_pass.py	Renames the test to include _vgf_ for VGF-only selection.
backends/arm/test/ops/test_custom_shader_lowering.py	Renames shader-lowering tests to include _vgf_ for VGF-only selection.
backends/arm/test/misc/test_custom_shader_payloads.py	Renames payload tests to include _vgf_ for VGF-only selection.

---

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[robell]

it seemed good to align versions for this - but if it's a problem we can drop this guidance back and just VGF requires newer. But 321 was getting a bit old so good to move.

[robell]

Since this is all Arm backend other than a 1 line doc change i'll go ahead as-is. and @SS-JIA we can revert the documentation suggested revision bump for glslc in vulkan backend.
The WebGPU failures appear on trunk and also in another unrelated change so it's pretty clear they're not introduced here.