[DataLoader] Adding `StackDataset` (#101338)
Torch wrapping datasets list has:
`TensorDataset`
`ConcatDataset`
`ChainDataset`
`TensorDataset` is useful for stacking sets of tensors but can't work with objects without `.size()` method.
This PR proposes `StackDataset`, similar to `TensorDataset` but for a general case like `ConcatDataset`.
Possible usage of `StackDataset` is multimodal networks with different input like image+text or for staking non-tensor input and property to predict.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101338
Approved by: https://github.com/ejguan, https://github.com/NivekT
