Unlift mutated buffers (#107643)
In this PR, we extend ExportedProgram.module() functionality by also unlifting the mutated buffers. We only really care about top level buffers as we don't allow any buffer mutation inside HigherOrderOps.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107643
Approved by: https://github.com/avikchaudhuri
