vk-layer-generate.py: add intercept_core_*_command
vk-layer-generate.py: add intercept_core_*_command

Replace layer_intercept_instance_proc with
intercept_core_instance_command, which returns all intercepted core
instance commands.

Replace layer_intercept_device_proc with intercept_core_device_command,
which returns all intercepted core device commands.

The only user visible difference should be that vkGetDeviceProcAddr now
returns NULL for instance commands.

Radamanthe/VulkanSamples,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,critsec/Vulkan-LoaderAndValidationLayers,KhronosGroup/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,critsec/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,KhronosGroup/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,elongbug/Vulkan-LoaderAndValidationLayers,Radamanthe/VulkanSamples,critsec/Vulkan-LoaderAndValidationLayers