Improve Vulkan initialization;
Improve Vulkan initialization;

- Check for layers before enabling
- Check for instance/device extensions before enabling

Fixes unfriendly errors when running on a system without validation layers
installed.

Uses same table approach as OpenXR code.

bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr,bjornbytes/lovr