Implement present from compute

[libcg]

BF4 wants to use this.

[libcg]

We use vkCmdBlitImage in the present path to convert the presentable image format to the swapchain format: games use R8G8B8A8 presentable images and X11 only allows B8G8R8A8 swapchains. Blits require a graphics queue.

Three ways forward:

• Assume Wayland (not realistic today)
• Use a compute shader to copy presentable image -> swapchain with swizzle
• Skip present copy entirely