[GraphModule] Improve buffer registration during init (#53444)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53444
GraphModule construction has two options when constructing the base nn.Module: a dict of names to attrs to assign to the GraphModule, or another nn.Module to copy attrs from.
- For the dict case, add logic to explicitly register `nn.Tensors` that are not `nn.Parameter` as buffers on the GraphModule, else fall back to `__setattr__`.
- For the other `nn.Module` case, update so that it checks in the other module whether the attr to copy in is a buffer, and register it as such, else fall back to `__setattr__`.
Test Plan: Added tests for fetching params and buffers from a GraphModule using both dict and module `__init__`s
Reviewed By: jamesr66a
Differential Revision: D26860055
fbshipit-source-id: 8d9999f91fef20aaa10969558006fc356247591f
