Implement portable abs for complex input

[pytorchbot]

This PR was created by the merge bot to help merge the original PR into the main branch.
ghstack PR number: #8146
^ Please use this as the source of truth for the PR details, comments, and reviews
ghstack PR base: https://github.com/pytorch/executorch/tree/gh/swolchok/228/base
ghstack PR head: https://github.com/pytorch/executorch/tree/gh/swolchok/228/head
Merge bot PR base: https://github.com/pytorch/executorch/tree/main
Merge bot PR head: https://github.com/pytorch/executorch/tree/gh/swolchok/228/orig
@diff-train-skip-merge

[pytorch-bot]

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• ROCM Infra failures during checkout of PyTorch

❌ 2 New Failures, 4 Pending, 1 Unrelated Failure

As of commit 9817e0a with merge base a5c7609 ():

NEW FAILURES - The following jobs have failed:

• Check Labels / Check labels (gh)
  RuntimeError: Error checking labels: PR does not have required labels
• pull / unittest / macos / macos-job (gh)
  examples/models/test/test_export.py::ExportTest::test_vit_export_to_executorch

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

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

• pull / unittest-arm / linux-job (gh) (trunk failure)
  backends/arm/test/ops/test_mm.py::TestMM::test_mm_single_input_tosa_BI_3

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