Add render API for resourcepacks and datapacks when migrating to Vulkan.

At the moment, Minecraft provides a large number of features for datapack and resource pack creators (and consequently for plugin developers). However, even simple things like dynamically rendering a 3D model already require creating a huge number of Text Display entities (4 entities per 1 polygon). Not to mention custom shaders, which currently require overriding existing ones through resource packs.

I propose adding the following features for datapack and resource pack creators:

• Native rendering both in 3D space and on 2D surfaces without the need to reload resources.

• The ability to add custom shaders to the rendering pipeline.

This would allow many servers to give players a gameplay experience that previously was only possible with third-party mods. (Technically, this was already possible before, but in practice everything would run into hardware limitations, since rendering hundreds of thousands of display entities could heavily load the computer. And, of course, because all of this happens server-side, the massive latency was also a problem.)