Creating a physical sky should also create a physical sun

[dictoon]

While it may be useful to create a standalone physical sun (e.g. to combine it with an HDR environment map), creating a physical sky without a corresponding sun is more questionable.

The idea here would be to always create a physical sun under the hood when a physical sky is used in the scene. The sun position would be controlled centrally and would affect both the physical sky and physical sun models.