[graph_manipulation] Set fused dtypes for all constant params/buffers (#77401)
Summary: We were handling constant attrs in a few different ways before, leading to confusion and missed handing for fused dtypes. This diff consolidates some of that code and unbreaks current breakage.
Test Plan: CI. Recently broken tests now pass.
Differential Revision: D36335238
Pull Request resolved: https://github.com/pytorch/pytorch/pull/77401
Approved by: https://github.com/jaybean-dev, https://github.com/jamesr66a
