[JIT] Add Context Manager to force strict fusion
Fixes https://github.com/pytorch/pytorch/issues/75464 Adds a context manager that will throw if the ops in the context are not fused.
API is :
```
with torch.jit.strict_fusion():
...
```
A few TODOs:
[+] Compose/figure out how to do with autodiff - right now it will run on autodiff as well
[+] Support all of the nvfuser operators that are added in guarding
[+] Figure out what to do with control flow that isn't taken (right now it will just error). this is probably a source of the original issue :/ - will just error
[+] (After those are figured out) add to docs
Pull Request resolved: https://github.com/pytorch/pytorch/pull/75777
Approved by: https://github.com/davidberard98
