Add test support for dynamic shapes for torch.onnx.dynamo_export (#106495)
This PR adds the ability to check whether the resulting ONNX graph has dynamic shape when the dynamic shape is enabled
Only test/onnx/test_fx_to_onnx.py and test/onnx/test_fx_op_consistency.py were covered because test/onnx/test_fx_to_onnx.py does not use any common "run_test" helper to wrap `dynamo_export` call. Maybe that could be a refactor
Pull Request resolved: https://github.com/pytorch/pytorch/pull/106495
Approved by: https://github.com/BowenBao
