More granular Sun & Sky settings

Right now, there are some (reasonable) implicit effects of certain settings that are not always obvious, expected, or noticed:

- Fog Distance: one setting controls where the lighting-fog begins, where the opacity-fog begins, and where it all ramps up to nothing being visible at all. This hides that the setting affects those things, and gives the creator less flexibility for the look of their scene, and also how it's optimised (for not rendering things beyond a certain distance).

- Sun Tint, Sky Tint: For more stylised games (which often means simpler games, which often means games created by new creators)... it's often desired to have a non-realistically-shaded background (eg. solid colour) just so it looks cool. Or change the colour of the sun to look funky.

But if they do that with these settings, the lighting of the scene itself takes on those colours too, which is almost never what they wanted in those situations. So then they need to use special methods to cover up the sun and sky just to have reasonable lighting but also the sky looking how they want it to look. Having a toggle to separate out the lighting itself from the visuals of the sun & sky would give creators more flexibility, and let new creators use the obvious settings instead of needing to ask someone how to do it.

- Shadow Scale: This has an implicit curve to mapping distance to shadow-resolution. It renders higher-detail shadows up to a fraction of the overall map, lower beyond that, etc. Having more control over this would allow us to have good detail shadows starting further away from the camera, and again performance characteristics for more nuanced games. Eg. "isometric" views focussed on objects far from the viewpoint cannot have high-detail shadows even at max settings, even though a fairly small area would need shadow-mapping.

These additions could theoretically require not much work; simply separating settings out for these things in the engine, instead of them implicitly affecting each other. And it would give us a lot more flexibility and enable building more custom experiences easier and with more subtlety.