layers: Add missing/disabled extension validation
layers: Add missing/disabled extension validation

Many of the main validation checks were ifdef'd out or were missing
entirely.

Change-Id: I18cd977a6a790cc12988c55093d826ab9ec50556

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