Use master weights for bfloat16 FusedAdam when master_weights=True #1731
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As mentioned in #1728, the FusedAdam optimizer ignores
master_weights=True
for bfloat16 parameters. This PR fixes that oversight. I have confirmed that the behavior now matches a "by hand" implementation of master weights (hand-copying) along with vanilla torch.optim.AdamW on the fp32 copy.