Add lighting

[erlend-sh]

Could maybe be split up into ‘basic lighting’ and ‘fancy lighting’.

Prior art:

• FallingSandEngine lighting shaders: lighting_prep.comp/lighting_propagate.comp/chunk_light.frag
• FancyLighting-Terraria
• 2D global illumination with radiance cascades at ~0.3 ms per frame
• https://github.com/zaycev/bevy-magic-light-2d
• https://github.com/ABC-Engine/lumenpyx/wiki/The-shadows-system