Use compile-time promotion to reduce optimized add/sub op size & build time (#3533)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/3533

Yet another pair of ops.

Reviewed By: manuelcandales

Differential Revision: D57023819

fbshipit-source-id: b3ce993c6926d0e1e277278e8a5a4638429a4a1e