Move to Vulkan

[Mirsario]

There are quite many unsatisfactory points about continued use of OpenGL, especially for a cross-platform engine:

• OpenGL drivers are generally quite buggy and differ in behavior between driver vendors, with some drivers having breakages, and some drivers having things that shouldn't be working in reality work quite flawlessly, creating a ton of "it works on my machine" scenarios. OpenGL also runs quite poorly on AMD Windows drivers, since, from what I heard, they just made that driver wrap over DirectX's.
  Meanwhile, Vulkan doesn't even leave that much work to the drivers for the drivers to be able to fail as hard.
• Apple has ceased OpenGL driver development, leaving Mac with already super outdated OpenGL 4.1, that too will disappear in the future. Screw Apple. Because of this, developers can't make use of Compute Shaders (required for implementation of Forward+ rendering pipeline), SPIR-V shader pre-compilation (lets people avoid a ton of GLSL-related driver bugs), and many other features.
  Meanwhile, Vulkan can run on Mac in pretty much full capacity using opens-source MoltenVK project. The OpenGL alternative, MoltenGL, is 100% proprietary.
• OpenGL is an overly simplified graphics API with a ton of limitations. I would like to look into the possibility of making the engine not have a main thread, but that is counter-productive with OpenGL.
  Meanwhile, this is fully achievable on Vulkan, as proven by idTech 7 (DOOM Eternal.) And they don't even have to deal with binding textures!