SL-18190 WIP -- Take 2 on linear space windlight (more methodical approach -- make desired interface but brute force color conversions). Placeholder PBR water and move to deprecate forward rendering shaders.

SL-14731: Fix sun gamma -- merge Sovereign Engineer's patch: Fix sun gamma space for accurate color reproduction of sun textures

Removed some potential div-by-0 NaNs and a mangled clamp.

Had to find a balance in the sunlight intensity calculation that behaves correctly for
both these issues.

WIP - Windlight sun lighting should happen in sRGB space, not linear space.  This keeps ambient from getting overblown and better matches environment lighting with ALM on/off.

The un-water-fogged gap area was rendering while we were still above water, but the water surface was being near culled.

I've re-enabled preculling water objects (which also fixes issues with water culling vs spinning the camera) and it seems to behave correctly.

Remove all references to unused shader var global_gamma.

Remove many unused decls for gamma from shaders.

Make post-deferred gamma correction use display_gamma.

Make setting display_gamma use the correct RenderDeferredDisplayGamma setting.

Make fullbright rigged objects with alpha mode none use fullbright shader instead of incorrectly using the material shader.

Increase effect of variance in cloud shaders.

Modified windlight shader to remove adjustment to glow.z

Make sun additive contribition depend on facing the sun (without breaking fog).

Put back scaling factor keeping sun contrib from blowing out with new FS param range for glow.

Fix emissives without normal maps clobbering the alpha output in materialF.

Modify glow size calc to get close to pre-EEP sun glow behavior (may require sky vert settings >= mid).

Make bake ignore alpha readback for Intel until we can determine why their drivers now go boom.

Make fullbright alpha mask with mask cutoff == 0 not generate shadows.

Adjust handling of ambient across forward and deferred again.

More tweaking ambient light.

Clamp fog distance multiplier to >= 0.05 and adjust min range on control as well.

Make sky shaders use dist mul consistently.

Fix light atten and transmittance calcs breaking ambient color contrib to fog.

Needs to be tested on DRTSIM-415 or better to get legacy viewer settings that match EEP.

Modify ambient handling and forward projector lighting again to stamp out alpha fires.

Fix ambient light inputs to the renderer.

Fix 3rd sky shader w/ mistaken density mod conversion.

Make ambient clamp apply to all modes.

Tune ALM ambient clamp to match non-ALM.

Adjust ambient clamp up to get closer match to release viewer for existing content.

Modify calc of sunlight to avoid clipping in gamma correct on values outside 0-1 range.

Modify shaders to put back ambient clamp tuned to be close to ambient contrib in low/mid lighting.

Make haze look more like WL.

Make lack of sun and moon mean black and fixed dir to prevent spooky underlighting.

Fix direct light matching across alpha/blended-material/deferred.

Get diffuse lighting to match from Low to Ultra.

Consistency across class2/3/ALM lighting.

Put ambient clamp threshold back for lighter shadows but closer match to release lighting.

Fix handling of 1/light_y when y was tiny but getting even tinier.

Add similar adjustment to shader version of same calc.