[ET-VK][qconv] Read weight buffer as int in pack_q8_conv2d_weights shader

[SS-JIA]

Stack from ghstack (oldest at bottom):

• [ET-VK][testing] Add ETVK_FORCE_NO_EXTENSIONS debug flag #17692
• [ET-VK][qconv] Add software fallback for dotPacked4x8AccSatEXT in q8ta_ shaders #17691
• -> [ET-VK][qconv] Read weight buffer as int in pack_q8_conv2d_weights shader #17690

The shader previously declared the input weight buffer as int8, requiring
the GL_EXT_shader_8bit_storage extension which is not supported on all
devices. Replace with an int (int32) buffer and extract individual bytes
via shift-and-mask, the same technique used in nchw_to_int8x4_buffer.glsl.
This makes the shader functional on devices without 8-bit buffer support.

Differential Revision: D94314255

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17690

• 📄 Preview Python docs built from this PR

Note: Links to docs will display an error until the docs builds have been completed.

❌ 4 New Failures, 1 Cancelled Job

As of commit eca2a0d with merge base 63f9724 ():

NEW FAILURES - The following jobs have failed:

• Propose to merge ghstack orig PRs to main / Try to create a PR with ghstack /orig branch (gh)
  Process completed with exit code 1.
• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 9a6fecfabeeb122cd121fffd7ef8bb2c54fe142b998379077eb6d683d5fafdc8 /exec failed with exit code 1
• Test Metal Backend / export-model-metal-artifact (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-metal) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• Test Metal Backend / export-model-metal-artifact (nvidia, parakeet-tdt, non-quantized) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

CANCELLED JOB - The following job was cancelled. Please retry:

• pull / unittest-buck / macos / macos-job (gh)
  ##[error]The operation was canceled.

This comment was automatically generated by Dr. CI and updates every 15 minutes.

[github-actions]

This PR needs a release notes: label

If your change should be included in the release notes (i.e. would users of this library care about this change?), please use a label starting with release notes:. This helps us keep track and include your important work in the next release notes.

To add a label, you can comment to pytorchbot, for example
@pytorchbot label "release notes: none"

For more information, see
https://github.com/pytorch/pytorch/wiki/PyTorch-AutoLabel-Bot#why-categorize-for-release-notes-and-how-does-it-work.