Implement correction argument in torch.masked.{std,var} (#87118)
This makes the signature of `torch.masked.std` and `var` more consistent with the global namespace variant and also updates the sample inputs to repurpose the existing `sample_inputs_std_var` inputs which fully exercise the `correction` argument.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/87118
Approved by: https://github.com/cpuhrsch
