This code was being generated in both Vulkan-ValidationLayers
and Vulkan-ExtensionLayer. Further uses are on the horizon so
lets stop the copypasta.
Also, add functions to manipulate extension lists and pNext chains,
since many client layers have been doing that themselves.
- Update known-good
- Generate source
- Remove vk_layer_settings_ext.h
- Change all usage of VkLayerSettingEXT::count to use the new name
valueCount from the public header.
