NXP backend: Test avg_pool2d with new Neutron flow.

[MartinPavella]

Summary

Add tests verifying correct support for avg_pool2d by the Neutron backend using the new Neutron MLIR flow.

Test plan

Unit tests provided.

cc @robert-kalmar @JakeStevens @digantdesai

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/executorch/19147

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❌ 3 New Failures, 3 Cancelled Jobs

As of commit 3a45298 with merge base 8a97ac7 ():

NEW FAILURES - The following jobs have failed:

• pull / test-qnn-delegate-linux / linux-job (gh)
  backends/qualcomm/tests/test_qnn_delegate.py::TestQNNFloatingPointOperator::test_qnn_backend_argmin
• pull / unittest / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1
• pull / unittest-editable / macos / macos-job (gh)
  RuntimeError: Command bash /Users/ec2-user/runner/_work/_temp/exec_script failed with exit code 1

CANCELLED JOBS - The following jobs were cancelled. Please retry:

• pull / test-models-linux (mobilebert, portable, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-models-linux (mobilebert, xnnpack-quantization-delegation, linux.2xlarge) / linux-job (gh)
  ##[error]The operation was canceled.
• pull / test-voxtral-realtime-xnnpack-linux / linux-job (gh)
  ##[error]The operation was canceled.

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[MartinPavella]

Internal CI: https://bamboo3.sw.nxp.com/browse/MLTECE-EXIGH141-5

[github-actions]

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[jirioc]

Note that neutron unit tests are failing.