tests: Update NonCoherentMemoryMapping with new case
tests: Update NonCoherentMemoryMapping with new case

Add case to NonCoherentMemoryMapping test where regions with two separate
offsets are flushed from a mapped region to verify that offset of flush
region does not incorrectly affect validation of mapped region overrun.

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