Add support for creating VK_KHR_DISPLAY compositors (e.g. Wayland) with Godot

[theoparis]

Describe the project you are working on

I want to make a custom window manager/compositor using Vulkan and I figured Godot would make my life easier. This would also benefit GodotOS, see popcar2/GodotOS#1.

Describe the problem or limitation you are having in your project

I cannot run a godot game directly on the display. I can certainly use a barebones wayland compositor such as Cage once godot finishes wayland support, or an X11 server however that means I'd have to run two wayland compositors at once on top of one another.

Describe the feature / enhancement and how it helps to overcome the problem or limitation

Supporting VK_KHR_DISPLAY could possibly solve #6364 but instead of it being Linux only, it would be cross platform (Windows supports VK_KHR_DISPLAY from what I've seen).

Describe how your proposal will work, with code, pseudo-code, mock-ups, and/or diagrams

I'm not entirely sure what the best way to implement this would be, however I thought that it could be implemented as a display driver backend (along with headless and x11).

If this enhancement will not be used often, can it be worked around with a few lines of script?

It can be worked around using an existing, minimal wayland kiosk such as Cage (cage -- my-de) once Godot adds wayland support.

Is there a reason why this should be core and not an add-on in the asset library?

It would be adding to the core rendering code.