layers: Tidy up tracking of enabled device extensions in CV
layers: Tidy up tracking of enabled device extensions in CV

- These are all guaranteed initialized.
- Convert code to data.

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