[experimental][ET-VK][qconv] Use specialization constants for conv2d params in q8ta shaders

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [experimental][ET-VK][qconv] Use specialization constants for conv2d params in q8ta shaders #18163

Replace Conv2DParams UBO with specialization constants in q8ta_conv2d,
q8ta_conv2d_dw, and q8ta_im2col shaders. This allows the GPU compiler to
treat conv params (kernel size, stride, padding, dilation, groups) as
compile-time constants, enabling loop unrolling, dead code elimination,
and constant folding.

Differential Revision: D96503584

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/18163

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❌ 8 New Failures, 8 Unrelated Failures

As of commit 92d132d with merge base cc27e6b ():

NEW FAILURES - The following jobs have failed:

• Build Presets / windows (pybind) / build (gh)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Build Presets / windows (windows) / build (gh)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Test CUDA Builds / check-all-cuda-builds (gh)
  Process completed with exit code 1.
• Test CUDA Builds / export-model-cuda-artifact (google, gemma-3-4b-it, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t bd30e44fe60f28608b19fc911c15589bf2992c4ae96ea196c216a9d9d5f27f99 /exec failed with exit code 1
• Test CUDA Builds / export-model-cuda-artifact (openai, whisper-small, quantized-int4-tile-packed) / linux-job (gh)
  RuntimeError: Command docker exec -t 5e5636ca0d193cd0a0ff7f9b895b9b70edfee31aa72f5bdfc47d8c9d39f6780f /exec failed with exit code 1
• Test CUDA Builds / test-executorch-cuda-build-12.9 / linux-job (gh)
  RuntimeError: Command docker exec -t 3cc0d0fbed784f5b59b43eeb0080a8eb65ee5f280353ede70ace91c670316933 /exec failed with exit code 1
• Test CUDA Builds / test-models-cuda (linear) / linux-job (gh)
  RuntimeError: Command docker exec -t 54c8d05d21d7effefede72258ba57aaf285d9b995828af69c91beec48db27035 /exec failed with exit code 1
• Test CUDA Builds / unittest-cuda / linux-job (gh)
  backends/cuda/tests/test_output_stride_rearrange.py::TestOutputStrideRearrange::test_fast_path_no_mask

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

• pull / unittest / windows / windows-job (gh) (similar failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1

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

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

• pull / unittest-editable / windows / windows-job (gh) (trunk failure)
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (mistralai, Voxtral-Mini-3B-2507, non-quantized) / windows-job (gh) (trunk failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / windows-job (gh) (trunk failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (mistralai, Voxtral-Mini-4B-Realtime-2602, quantized-int4-tile-packed) / windows-job (gh) (trunk failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (nvidia, diar_streaming_sortformer_4spk-v2, non-quantized) / windows-job (gh) (trunk failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (nvidia, parakeet-tdt, non-quantized) / windows-job (gh) (trunk failure)
• Test CUDA Windows Export and E2E / test-model-cuda-windows-e2e (nvidia, parakeet-tdt, quantized-int4-weight-only) / windows-job (gh) (trunk failure)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1

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