Set a unit for lighting.

[schell]

We don't yet use a unit for our lighting, and we should.
https://www.realtimerendering.com/blog/physical-units-for-lights/
NOTE:
glTF spec [1] says directional light is in lux, whereas spot and point are
in candelas. I haven't really set a unit, it's implicit in the shader, but it seems we
can roughly get candelas from lux by dividing by 683 [2].

1. https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_lights_punctual/README.md
2. https://depts.washington.edu/mictech/optics/me557/Radiometry.pdf
   

   renderling/crates/renderling/src/stage/gltf_support.rs

   Lines 1007 to 1016 in 1ab3eeb

   	// TODO: Set a unit for lighting.
   	// We don't yet use a unit for our lighting, and we should.
   	// NOTE:
   	// glTF spec [1] says directional light is in lux, whereas spot and point are
   	// in candelas. I haven't really set a unit, it's implicit in the shader, but it seems we
   	// can roughly get candelas from lux by dividing by 683 [2].
   	// 1. https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_lights_punctual/README.md
   	// 2. https://depts.washington.edu/mictech/optics/me557/Radiometry.pdf
   	intensity: intensity / 683.0,
   	});