Expose lighting variables for eevee

It is currently not possible to write an actual shader, that does shading with eevee.

Because in order to do lighting calculations, I kind of have to know things like the incoming normal, the color or the intensity of a light source.

And since eevee has to know these things in order for the pre-built shader nodes to work, it'd be nice to have access to these variables as a user.

Admittedly, there are some weird workarounds with drivers, that you can manually do for each light source, but it's pretty cumbersome and frustrating to write a shader that way.