tests: Clean cmath and climits usage
tests: Clean cmath and climits usage

- remove usage of `limits.h` that should not have existed
- merge the two separate handling of `nextafter` direction
- remove workaround for `cmath` impls with missing `std::`

KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers