Test int64 dtype (#3728)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3728

Using the `I64toI32()` export pass, we now support i64 input and constants (tensors defined in the `nn.Module`) and we test the following cases:
- `torch.randint()` i64 input
- `torch.tensor()` i64 input / constants
- `torch.arange()` i64 input / constants

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ghstack-source-id: 229458711

Reviewed By: SS-JIA

Differential Revision: D57649649

fbshipit-source-id: 3b69d456ebdce1f9c2f855614a4723feb469ae62