When FileCheck is destructed without execution, it should output all rules.
For example:
```
>>> fc = FileCheck().check("test")
>>> del fc
You have not run this instance of FileCheck!
FileCheck checks:
CHECK: test
```
Additionally, unit tests for the Python interface of FileCheck will be added.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/135345
Approved by: https://github.com/eellison
