tests: Add test for consuming COMBINED_IMAGE_SAMPLER as both
tests: Add test for consuming COMBINED_IMAGE_SAMPLER as both

Explicitly allowed by 13.1.4. This upsets the validation a little, as
until now it's assumed that there cannot be two variables live for a
single descriptor binding slot.

Signed-off-by: Chris Forbes <c3279c50043e18e9442c1ae071cafa0e7a4ca967@google.com>

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