[fx splitter] Fix fusion group utility (#57280)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/57280
We've found an issue that fusion group would results in circular dependency. For example
```
a -> b -> c -> d
| ^
+ -------------+
Only a has non tensor output and currently we would create a fusion group (a, b, d). This results in circular dependency because now the fusion group depends on c while c depends on the fusion group as well.
```
This diff implement the solution discussed before. When we add a node to fusion group, we add all the nodes that are in the middle of the fusion group and this newly added node.
Use the same logic in minimizer to build fusion group.
Test Plan: split_tests and net_min_tests
Reviewed By: khabinov
Differential Revision: D27917432
fbshipit-source-id: a3d99fe5929dbc9f8eb0f45bccd83fd7b173795a
