Remove use of ET_EXTACT_SCALAR in portable kernels (#1683)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1683

Ensure that dtypes are compatible in op checks, then replace uses of ET_EXTRACT_SCALAR with utils::extract_scalar.

Reviewed By: manuelcandales

Differential Revision: D53004484

fbshipit-source-id: 6deda6cc478981aad1b374f6089ced7835eeeb71