Support functionalization on torch.cond (#89966)
This PR adds functionalization path for torch.cond. As it is the first pass, we only functionalize for very restrictive use cases. We explicitly restrict following:
- Output of each branch aliasing input
- In-place mutation on inputs given to each branch
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89966
Approved by: https://github.com/zou3519
