[Rendering] Rendering optimisations v2

[kanerogers]

Background

After getting significant gains in #226, there's still much more juice we can squeeze out of the renderer.

The name of the game is bandwidth. We must ensure that we pull as little data down as possible in each draw.

TODO

• [Rendering] LODs #357
• Use instancing (Qualcomm recommends this: https://developer.qualcomm.com/sites/default/files/docs/adreno-gpu/developer-guide/gpu/best_practices_vertex.html#consider-geometry-instancing)
• [Rendering] Use 16bit data types on the GPU where possible #356
• [Feature] Implement fixed-foveated rendering #274
• https://www.unrealengine.com/en-US/blog/physically-based-shading-on-mobile
• https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_texture_transform/README.md