cuda/cpu: Increase support for fp16 unary operations (ggml/1125)

* Support fp16 unary operations in the CUDA backend

* cpu: increase fp16 support for unary operators in the CPU backend

* cuda: increase fp16 support for unary operators in the CUDA backend

* Add test cases for fp16 unary operators

* metal: update supports_op for unary operators that don't support fp16, to prevent test-backend-ops from failing

* metal: fix PR comments for unary op support after fp16 unary tests

Author: cmdr2