[DTensor] Initialized RNG tracker if needed (#121328)
Since we are already checking if the RNG tracker is initialized, there is no real performance difference between erroring vs. just initializing a default RNG tracker (which we choose to be the `OffsetBasedRNGTracker`).
```
pytest test/distributed/_composable/fsdp/test_fully_shard_init.py -k test_meta
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121328
Approved by: https://github.com/wanchaol
ghstack dependencies: #120351
