Half support: unary ops with realhb to bool pattern (2 ops) (#1708)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1708

Updated the following 2 ops to support Half dtype:
- isinf
- isnan
ghstack-source-id: 213131135
exported-using-ghexport

Reviewed By: mikekgfb

Differential Revision: D53074458

fbshipit-source-id: 24d1f0f9248a576f0d0bd478569914954b5a4fe8