Deify opmath_t into its own header, align with accscalar_t (#63986)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/63986
Fixes #63985
Signed-off-by: Edward Z. Yang <ezyang@fb.com>
Test Plan: Imported from OSS
Reviewed By: malfet
Differential Revision: D30555996
Pulled By: ezyang
fbshipit-source-id: b6e4d56a5658ed028ffc105cc4b479faa6882b65
