Fixes#147140
## Changes
- Add `to` implementation in `MaskedTensor` to support move `mask` to target device
## Test Result
```python
In [1]: import torch
...: from torch.masked import as_masked_tensor
...: data = torch.tensor([1,2,3])
...: mask = torch.tensor([True,False,True])
...: mt = as_masked_tensor(data, mask).to('cuda')
...: mt.get_data().device, mt.get_mask().device
/home/zong/code/pytorch/torch/masked/maskedtensor/core.py:247: UserWarning: The PyTorch API of MaskedTensors is in prototype stage and will change in the near future. Please open a Github issue for features requests and see our documentation on the torch.masked module for further information about the project.
return MaskedTensor(data, mask)
/home/zong/code/pytorch/torch/masked/maskedtensor/_ops_refs.py:354: UserWarning: The PyTorch API of MaskedTensors is in prototype stage and will change in the near future. Please open a Github issue for features requests and see our documentation on the torch.masked module for further information about the project.
return MaskedTensor(new_data, _maybe_get_mask(args[0]))
Out[1]: (device(type='cuda', index=0), device(type='cuda', index=0))
In [2]: mt.sum(dim=0)
/home/zong/code/pytorch/torch/masked/maskedtensor/core.py:247: UserWarning: The PyTorch API of MaskedTensors is in prototype stage and will change in the near future. Please open a Github issue for features requests and see our documentation on the torch.masked module for further information about the project.
return MaskedTensor(data, mask)
Out[2]: MaskedTensor(4, True)
```
```bash
pytest test/test_maskedtensor.py -vv
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/151205
Approved by: https://github.com/ezyang
216ba6e5f2