[fx splitter][fx net_min] Move Splitter, Minimizer and necessary deps to OSS (#56201)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56201
Refactor Splitter and Minimizer to superclass `_SplitterBase` and `_MinimizerBase` and move them to OSS. This is needed to create an OSS example of GPU lowering with those tools.
Test Plan: CI
Reviewed By: jackm321
Differential Revision: D27629598
fbshipit-source-id: 0d4da02105ca509b31f1a6c4a39b1122c2bc7bf0
