layers: Add VK_KHR_external_semaphore_fd functions
layers: Add VK_KHR_external_semaphore_fd functions

Add entry points and wire up to existing validation in place for
VK_KHR_external_semaphore_win32

Change-Id: I82da27d6a68c7b4eea3f01b4dd4fa0ce38d97f0b

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