[quant][graphmode][fx] Add support for weight prepack folding (#43728)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43728
Trace back from the weight node util we hit getattr, reconstruct the graph module with the traced nodes
and run the graph module to pack the weight. then replace the original chain of ops with the packed weight.
Test Plan: Imported from OSS
Reviewed By: vkuzo
Differential Revision: D23385090
fbshipit-source-id: 11341f0af525a02ecec36f163a9cd35dee3744a1
