[fx][split] Copy node metadata for placeholders (#107981)
- Follow-up to #107248 which copies metadata for placeholder nodes in the top-level FX graph
- Currently, top-level placeholders do not have their metadata copied over, causing loss of `TensorMetadata` in some `torch.compile` backends
Fixes https://github.com/pytorch/TensorRT/issues/2258
Pull Request resolved: https://github.com/pytorch/pytorch/pull/107981
Approved by: https://github.com/angelayi
