[ExecuTorch][WebGPU] Add view_copy op (aten.view_copy.default)

[JulianCloudNTH]

Stack from ghstack (oldest at bottom):

• [ExecuTorch][WebGPU] select_copy op test suite (cases.py op-test framework) #20363
• [ExecuTorch][WebGPU] Add select_copy op (aten.select_copy.int) #20362
• [ExecuTorch][WebGPU] view_copy op test suite (cases.py op-test framework) #20361
• -> [ExecuTorch][WebGPU] Add view_copy op (aten.view_copy.default) #20360
• [ExecuTorch][WebGPU] mul op test suite (cases.py op-test framework) #20359
• [ExecuTorch][WebGPU] Add mul op with full broadcast (aten.mul.Tensor) #20358
• [ExecuTorch][WebGPU] Consolidate landed-op tests into the cases.py op-test framework #20357
• [ExecuTorch][WebGPU] Op-test codegen framework (cases.py -> generated .pte+golden -> gtest driver) #20339

Adds aten.view_copy.default to the WebGPU delegate. A contiguous reshape on a dense row-major buffer backend is a flat copy output[i] = input[i], so the op is a single 1D-dispatch copy kernel.

Composition (single compute dispatch):

• runtime/ops/view_copy/view_copy.h — declares add_flat_copy(graph, in_id, out_id): fail-loud guards (both tensors, fp32, numel-preserving) + the view_copy.wgsl dispatch over compute_1d_workgroup_count(num_elements) with override wg_size; mirrors Vulkan add_view_copy_node.
• runtime/ops/view_copy/ViewCopy.cpp — reads args = [self, size, out], ignores the AOT-fixed size value-id (output shape comes from out_tensor.dims), calls add_flat_copy.
• runtime/ops/view_copy/view_copy.wgsl — guards idx >= num_elements, writes output[idx] = input[idx].
• add_flat_copy is factored into the header so the stacked squeeze/unsqueeze ops reuse it without a new kernel.

Differential Revision: D108793164

[pytorch-bot]

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❌ 1 New Failure, 1 Cancelled Job, 1 Unrelated Failure

As of commit 1175a70 with merge base eb7473b ():

NEW FAILURE - The following job has failed:

• pull / test-arm-backend-no-driver (test_pytest_models_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t 2573962e3aa92327a36aa11c1d05cd8471bafb22bc76251b156839accda11ab6 /exec failed with exit code 1

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

• pull / unittest-nxp-neutron / linux-job (gh)
  ##[error]The operation was canceled.

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

• pull / test-moshi-linux / linux-job (gh) (matched linux rule in flaky-rules.json)
  E: Failed to fetch http://archive.ubuntu.com/ubuntu/pool/main/m/mesa/mesa-vdpau-drivers_23.2.1-1ubuntu3.1%7e22.04.3_amd64.deb 404 Not Found [IP: 104.20.28.246 80]

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