[jit] Unify augmented assign handling (#33578)
Summary:
Stacked PRs
* **#33578 - [jit] Unify augmented assign handling**
* #32993 - [jit] Fix aug assign for non-tensor attributes
We handle augmented assignments to `Select` and `Var` statements differently, but the actual in place update is the same for both, so this PR factors it out into a method so we don't have 2 code paths doing the same thing.
](https://our.intern.facebook.com/intern/diff/20010383/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33578
Pulled By: driazati
Differential Revision: D20010383
fbshipit-source-id: 52e559ce907e95e5c169ab9d9690d0d235db36f3
