Blender Git Loki

Eevee: Add partial support for the Light Path Node

This makes it possible to tweak indirect lighting in the shader.

Only a subset of the outputs is supported and the ray depth has not exactly
the same meaning:

Is Camera : Supported.
Is Shadow : Supported.
Is Diffuse : Supported.
Is Glossy : Supported.
Is Singular : Not supported. Same as Is Glossy.
Is Reflection : Not supported. Same as Is Glossy.
Is Transmission : Not supported. Same as Is Glossy.
Ray Length : Not supported. Defaults to 1.0.
Ray Depth : Indicate the current bounce when baking the light cache.
Diffuse Depth : Same as Ray Depth but only when baking diffuse light.
Glossy Depth : Same as Ray Depth but only when baking specular light.
Transparent Depth : Not supported. Defaults to 0.
Transmission Depth : Not supported. Same as Glossy Depth.

Caveat: Is Glossy does not work with Screen Space Reflections but does work
with reflection planes (when used with SSR or not).
We have to render the world twice for that to work.