text: Title: FSDPPrecision should support 16-true with a loss scaler
  Body: ### Description & Motivation
  
  https://github.com/Lightning-AI/pytorch-lightning/blob/f6fd046552a1504023cb3386a8a0df418a810e4f/src/lightning/fabric/plugins/precision/fsdp.py#L61
  
  
  What if I want to use fp16 true, but with a loss scaler? This is closer to DeepSpeed's default settings. With FSDP, 16-true, no loss scaler my model doesn't converge. However, with FSDP, 16-true, and a loss scaler (commented out the assert and fixed the typo'ed return scaler instead of return none line) my model converges.
  
  ### Pitch
  
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  ### Alternatives
  
  _No response_
  
  ### Additional context
  
  _No response_
  
  cc @borda