Vulkan support for the overlay (Windows/Linux)

The overlay should be updated to support Vulkan.

On Windows and Linux, NVidia's Vulkan support is built on top of their existing GL driver. Thus, the current GL overlay might already work for NVidia cards.

For a native experience, the easiest thing to target for Vulkan would presumably be Intel integrated graphics on a Linux system. This should do for a POC.

Once we have a POC for Linux, this should be ported to Windows as well.