[ONNX] Refactor AvgPool to support dynamic shapes (#105683)
In #87892, to pick up the corner cases found in #71549, the PR falls back the implementation of AvgPool to the way opset 9 implementing. However, it introduces a regression on dynamic shape cases found in #101397. This PR refactors the AvgPool op with the same implementation we have in onnxscript: https://github.com/microsoft/onnxscript/pull/754.
However, the corner case with `count_include_pad` remains unsolved in onnxruntime: https://github.com/microsoft/onnxruntime/issues/16203. The calculuation on the last value of each dimension is different between ORT and PyTorch. But the fix can be proved in: https://github.com/microsoft/onnxruntime/pull/16752, and it supports AvgPool since opset19.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105683
Approved by: https://github.com/thiagocrepaldi
