[ONNX] Export split with list of sizes (#33161)
Summary:
Exporting Split with a dynamic list of split_sizes is not supported.
This PR enables export using onnx SplitToSequence + SequenceAt
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33161
Reviewed By: hl475
Differential Revision: D19860152
Pulled By: houseroad
fbshipit-source-id: 300afedc22b01923efb23acd1a3627aa146bb251
