Add convenience switch macros (#1702)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1702

Added convenience switch macros for:
- FLOATH = Float + Half
- REALH = Real + Half
- REALB = Real + Bool
- REALHB = Real + Half + Bool

Updated add op in order to test macros
ghstack-source-id: 213130881
exported-using-ghexport

Reviewed By: mikekgfb

Differential Revision: D53061770

fbshipit-source-id: b6d648211fd7cb929ee9732e9fd39248205061f8