[spmd compile api] use fake tensor for DTensor propagation (#98789)
Summary: When using real tensors for DTensor propagation, functionalized _fuse_adam causes a memory spike of size(params + optim_state), which causes OOM on memory constrained environments.
Test Plan: Tested manually.
Differential Revision: D44845043
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98789
Approved by: https://github.com/mrshenli
