Fakify params and weights under private config (#90417)
Previously, we planned to lift the parameters and weights while exporting and implement our own transformer to "unlift" the lifted weights and params back to the graph as attributes. But this is bit challenging because:
- We need to maintain correct ordering for weights and parameters that are passed as inputs so that we know how to map them back.
- Some weights are unused in the graph, so our transformer needs to be aware of which weights and parameters are not used in the graph. And we need to distinguish which are real user input and which are parameters.
- There can be more edge cases we haven't seen in other models yet.
I am aware that @Chillee and @bdhirsh mentioned that functionalization won't work with fake-tensor attributes but this is fine for the short term as we don't expect users to be modifying weights and params in inference mode. In fact, we explicitly disable attribute mutation in torchdynamo export mode right now.
Given above condition, it might be ok to just fakify params when we need. I use a flag to guard against this change.
Differential Revision: [D41891201](https://our.internmc.facebook.com/intern/diff/D41891201)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90417
Approved by: https://github.com/eellison
