[Relay][Frontend][ONNX] Allow importing models with malformed Loop nodes. #8475
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A user recently noted that there are some issues importing some DLRM models generated by Pytorch in this thread. After investigating, I found that the problem is that Pytorch is generating loop nodes without proper output shape information, which causes us to use improper variable shapes. To fix this, we can instead do type inference on the loop body to figure out output shapes on our own. This should be more robust in general.
I've added a test case with a malformed loop node to confirm this fix works. I also removed an old warning that has since been fixed.