Framework: Support Vulkan::LayerSettings from Vulkan-Utility-Libraries

We currently have our own parsing for config files of JSON. I've been pointed at a standard library for this provided by Khronos, which supports both config file and configuration through the API. This seems like a useful capability improvement we should adopt, rather than rolling our own.

TBC how well this works on Android, but if we need to make changes we can contribute upstream.