Half support: unary ops with realhb to floath pattern (18 ops) (#1707)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1707

Updated the following 18 ops to support Half dtype:
- acos
- acosh
- asin
- asinh
- atan
- atanh
- cos
- cosh
- erf
- exp
- log
- reciprocal
- rsqrt
- sin
- sinh
- sqrt
- tan
- tanh
ghstack-source-id: 213130884
exported-using-ghexport

Reviewed By: mikekgfb

Differential Revision: D53074199

fbshipit-source-id: 82dc7216ddadd84f3d81bc1f503e5f98f5869421