Support tuples in ScriptModule inputs/outputs (#20784)
Summary:
- [x] Add tests after https://github.com/pytorch/pytorch/pull/20256 is merged
- Support exporting ScriptModule with inputs/outputs of arbitrarily constructed tuples.
- Moved the assigning of output shapes to after graph conversion to ONNX is completed. By then all tuples in the IR has already been lowered by the pass ```_jit_pass_lower_all_tuples```. If assigning output shapes is required to happen before that, we'll need to hand parse the tuple structures in the graph, and repeat the same logic in ```_jit_pass_lower_all_tuples```. Handling inputs is easier because all tuple information is encoded within the input tensor type.
- Swap the order of ```_jit_pass_lower_all_tuples``` and ```_jit_pass_erase_number_types```. Ops like ```prim::TupleIndex``` relies on index being a scalar. ```_jit_pass_erase_number_types``` will convert these kind of scalars to tensors.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20784
Reviewed By: zrphercule
Differential Revision: D15484171
Pulled By: houseroad
fbshipit-source-id: 4767a84038244c929f5662758047af6cb92228d3
