Fix build warning about deprecated debug utils user callback setter

[pH5]

Fix a build warning:

../src/vulkan_state.cpp:203:32: warning: ‘vk::DebugUtilsMessengerCreateInfoEXT& vk::DebugUtilsMessengerCreateInfoEXT::setPfnUserCallback(PFN_vkDebugUtilsMessengerCallbackEXT)’ is deprecated: This setter is deprecated. Use the one taking a function pointer type from the vk-namespace instead. [-Wdeprecated-declarations]

by moving the callback function type into the Vulkan namespace.