Ability to create and use device function pointers in vulkan.

Pointers with similar functionality to https://developer.apple.com/videos/play/wwdc2020/10013/ and to CUDA's device function pointers: https://leimao.github.io/blog/Pass-Function-Pointers-to-Kernels-CUDA/ , in addition to current https://nvpro-samples.github.io/vk_raytracing_tutorial_KHR/ but not restricted to raytracing.

Being able to create and use device pointers would be the first step to enable things like device generated *dispatch* for compute shaders. This is similar to how metal's functionality works (queues up addresses of pointers for workloads later).

The issue names no repository files, tests, or entry points. Start by comparing the requested device function-pointer capability with the linked Metal, CUDA, and ray-tracing references; the scope and acceptance criteria still need to be defined before implementation can begin.

Written by the indexing model from the issue text.