Investigate non-raytracing GI

[Anecoz]

Something better than a flat ambient term is needed for GI/indirect light when there is no ray-tracing support. It should ideally still be at least semi-dynamic.

Reflective shadow maps
Voxel Cone Tracing
Screen space GI

[Anecoz]

As of now, the idea is to "bake" light using DDGI into probe atlases. These atlases can be stored per tile. This would probably be the simplest way, since we can use the existing chain for using DDGI without ray tracing.

This would at least solve diffuse GI (but not allow for dynamic emissive meshes or directional light changes). For specular GI we probably need to look at something like baked reflection probes.