[executorch] Add propagate_input_spec pass and while_loop HOP support

[GregoryComer]

Stack from ghstack (oldest at bottom):

• [executorch] Update XNNPACK backend to use input_spec metadata + support HOPs #18147
• [executorch] Update delegation and partitioning to use input_spec metadata #18146
• [executorch] Rewrite remove_unused_parameters_pass for HOP support #18145
• -> [executorch] Add propagate_input_spec pass and while_loop HOP support #18144
• [executorch] Fix remove_clone_ops to prevent output aliasing #18143

Add a new pass named propagate_input_spec, which recursively assigns meta["input_spec"] on placeholder nodes, including in nested control flow submodules. Placeholders that don't correspond to a top-level input are not assigned this meta key. Also, add while_loop to get_control_flow_submodules.

Differential Revision: D95876986

[pytorch-bot]

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❌ 11 New Failures, 1 Pending, 1 Unrelated Failure

As of commit bfadd0c with merge base 48bd687 ():

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)
• pull / unittest / windows / windows-job (gh)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1
• pull / unittest-arm-backend-with-no-deps (test_pytest_ops_tosa) / linux-job (gh)
  RuntimeError: Command docker exec -t d139a86af096eeae73c848d1284dd8d583997b11a17c2f744feb554a26b68062 /exec failed with exit code 1
• pull / unittest-editable / windows / windows-job (gh)
  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, non-quantized) / windows-job (gh)
  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)
  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)
  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)
  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)
  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, quantized-int4-weight-only) / windows-job (gh)
  The process 'C:\Program Files\Git\cmd\git.exe' failed with exit code 1

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

• Test CUDA Builds / export-model-cuda-artifact (mistralai, Voxtral-Mini-3B-2507, quantized-int4-weight-only) / linux-job (gh) (detected as infra flaky with no log or failing log classifier)

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