layers: Refactor ClearColor/DSImage for pre/post
layers: Refactor ClearColor/DSImage for pre/post

Change-Id: Id055c26ca0ecb5012f96a7e8f474d598d6b46dfd

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