tests:Add ImmutableSamplerOnlyDescriptor test
tests:Add ImmutableSamplerOnlyDescriptor test

Bind descriptor set with only an immutable-sampler and verify that no
warning is flagged.

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