scripts:Fix doc validation for 8-col DB
scripts:Fix doc validation for 8-col DB

Update doc validation to read in the new VUID string and core|ext
columns of the vk_validation_error_database.txt.

KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools,KhronosGroup/Vulkan-Tools