Add deprecation warning for to_edge + to_backend workflow in XnnpackPartitioner

[leafs1]

Summary

This PR adds a deprecation warning in the XnnpackPartitioner to guide users away from the deprecated to_edge() + to_backend() workflow and toward the recommended to_edge_transform_and_lower() flow. We inspect the call stack in the partitioner to detect when the partitioner is called from the deprecated workflow and then print out a warning statement. This helps prevent issues that can arise from the deprecated workflow.

Test plan

Added tests testing the deprecation warning functionality in test_xnnpack_partitioner.py. Tests verify that the warning appears when using to_edge() + to_backend() and does not appear when using to_edge_transform_and_lower().

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/13209

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❌ 2 New Failures, 2 Unrelated Failures

As of commit a434ef9 with merge base 5797608 ():

NEW FAILURES - The following jobs have failed:

• Build documentation / build (buck2) / Build doc (gh)
  At least one of the pre-conditions you specified did not hold
• pull / test-moshi-linux / linux-job (gh)
  RuntimeError: Command docker exec -t f49d1414cd550a47c17273ad30e88ec9a43980273aa116489d78efb273bebf5f /exec failed with exit code 1

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

• pull / unittest-arm-backend-with-no-fvp (test_pytest_models) / linux-job (gh) (matched linux rule in flaky-rules.json)
  The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

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

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

• pull / test-openvino-linux / linux-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'quantized_decomposed' object has no attribute 'convert_element_type'

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[GregoryComer]

Nice tests.

[GregoryComer]

Looks great. Thanks for adding this.