add mixed data type support for GroupNorm (#81852)
1. If user uses amp to run bfloat16 models, `torch.autocast` will
keep module paramters in acc dtype which will leave `gamma` and`beta`
in float while input/output will be in bfloat16.
2. If user explicitly cast the model to bfloat16,
the input/output and gamma/beta will all be in bfloat16.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/81852
Approved by: https://github.com/jgong5, https://github.com/malfet
