Support Half/BFloat16 in op_allclose

Pull Request resolved: https://github.com/pytorch/executorch/pull/7766

We incorrectly required these types to be bitwise-identical rather than close.

(I had to develop this internally because the op_allclose_test doesn't run in OSS.)

Differential Revision: [D68366831](https://our.internmc.facebook.com/intern/diff/D68366831/)
ghstack-source-id: 262600586

Co-authored-by: Scott Wolchok <swolchok@meta.com>