Add shape fn for isnan (#82162)
### Description
Add shape fn for isnan
### Issue
This is for PyTorch/XLA Lazy code gen
### Testing
Ran `BUILD_CPP_TESTS=0 python setup.py install` without error
In python shell, ran:
```
>>> import torch
>>> torch.isnan(torch.tensor([1, float('nan'), 2]))
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/82162
Approved by: https://github.com/Krovatkin
