Arm backend: Add sign decomposition pass and test

[tbergkvist]

Decomposes sign into other operators.

cc @digantdesai @freddan80 @per @zingo @oscarandersson8218

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/12159

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⏳ 1 Pending, 4 Unrelated Failures

As of commit 56ec087 with merge base 29858b4 ():

FLAKY - The following jobs failed but were likely due to flakiness present on trunk:

• pull / test-models-linux-basic (vit, portable, cmake, linux.2xlarge, executorch-ubuntu-22.04-clang12) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)
• pull / test-selective-build-linux / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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

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

• trunk / test-models-linux-aarch64 (mobilebert, portable, linux.arm64.2xlarge) / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.
• trunk / test-models-linux-aarch64 (mobilebert, xnnpack-quantization-delegation, linux.arm64.2xlarge) / linux-job (gh) (trunk failure)
  ##[error]The operation was canceled.

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[tbergkvist]

@pytorchbot label "partner: arm"

[tbergkvist]

@pytorchbot label "release notes: arm"

[tbergkvist]

@pytorchbot label "ciflow/trunk"

[pytorch-bot]

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