[fx][split] make sure we copy node.meta over during split (#107248)
Summary: Previously when we create placeholder nodes for sub graph modules, we didn't copy node.meta over.
Test Plan: CI
Differential Revision: D48330866
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107248
Approved by: https://github.com/zyan0, https://github.com/houseroad, https://github.com/Neilblaze
