[ET-VK] Add aten.index.Tensor op and tests

[SS-JIA]

Stack from ghstack (oldest at bottom):

• -> [ET-VK] Add aten.index.Tensor op and tests #17710
• [ET-VK] Add Vulkan ops for skin segmentation and EdgeTAM models #17709
• [ET-VK][q8_ops] Add int8x4_buffer_to_nchw shader and refactor Int8x4Staging #17708
• [ET-VK][ez] Fix global workgroup size underflow for sub-4D tensors in block config dispatch #17707

Implements aten.index.Tensor for the Vulkan backend, supporting 1D
self tensors with exactly one non-None index tensor. Includes buffer
and texture GLSL shaders, C++ operator registration, and correctness
tests.

Also extends the op test code generators to handle
c10::List<::std::optional<at::Tensor>> (Tensor?[] in ATen), which
is the C++ type for the indices argument of aten.index.Tensor.

Differential Revision: D94364638

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/17710

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❌ 3 New Failures

As of commit f306d9a with merge base 63f9724 ():

NEW FAILURES - The following jobs have failed:

• pull / unittest-editable / macos / macos-job (gh)
  export/tests/test_target_recipes.py::TestTargetRecipes::test_mv3_model
• Test Metal Backend / test-model-metal-e2e (openai, whisper-large-v3-turbo, 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 / test-model-metal-e2e (openai, whisper-small, quantized-int4-metal) / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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[manuelcandales]

How about Bool vs Int? I think you are implementing the integer case only, right? If that's the case, also add a VK_CHECK_COND saying that only integer index is supported.