XNNPACK: Run recommended pre-partition transforms in AOT flow

[mansnils]

Wire get_transform_passes() into the XNNPACK example AOT compiler so official exports run the same recommended pre-partition graph transforms used by tests.

Update XNNPACK docs and README snippets to show the optional transform_passes stage and clarify that it is recommended in general for XNNPACK before partitioning.

cc @GregoryComer @digantdesai @cbilgin @freddan80 @per @zingo @oscarandersson8218 @Sebastian-Larsson @robell @rascani

[pytorch-bot]

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❌ 4 New Failures, 4 Unrelated Failures

As of commit f0f41be with merge base 82a605d ():

NEW FAILURES - The following jobs have failed:

• pull / unittest / linux / linux-job (gh)
  RuntimeError: Command docker exec -t a6665e4956a67465630db2c9e61984445441c965091c39e68b850c18810b9c3b /exec failed with exit code 1
• pull / unittest-editable / linux / linux-job (gh)
  RuntimeError: Command docker exec -t 9cc39d1e9cd2408d7240665cdfaa8512eaf744c79b5d828759411ca61abaf9e6 /exec failed with exit code 1
• trunk / test-llama-runner-qnn-linux (fp32, qnn_16a16w, qnn) / linux-job (gh)
  RuntimeError: Command docker exec -t a40a4b547bdb609c43a02fc695ec4291b619efc3507f13a4fca20e72c923d9f7 /exec failed with exit code 137
• trunk / unittest-release / linux / linux-job (gh)
  RuntimeError: Command docker exec -t a1397e66a33d5a80a737b0fbc9e192a6f8eaa7f4810044f99f98117f8acdcd3f /exec failed with exit code 1

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

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

• pull / test-llama-runner-qnn-linux (fp32, qnn_16a16w, qnn) / linux-job (gh) (trunk failure)
• pull / unittest / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• trunk / unittest-release / macos / macos-job (gh) (trunk failure)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

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