DRTVWR-559 Revert skies to be very close to release and disable tone mapping when probe ambiance is zero.

Hack for desaturating legacy materials has been removed for performance and quality reasons.

Adds a new setting for auto adjusting legacy skies.  This is the PBR "opt out" button.  If disabled, legacy skies will disable tonemapping, automatic probe ambiance, and HDR/exposure.  If enabled, legacy skies will behave as if probe ambiance and HDR scale are 1.0, and ambient will be cut in half.  

HDR scale will act as a sky brightener, but will automatically adjust dynamic exposure so the sky will be properly exposed.  If you want relatively even exposure all the time, set HDR Scale to 1.0.  If you want a high range of exposures between indoor/dark areas and outdoor/bright areas, increase HDR Scale.

Also tuned up SSAO (thanks Rye!).

Reviewed with Brad.

DRTVWR-559 Balance night scenes against release, nudge glow down a smidge, remove exposure correction from legacy fullbright balance PBR materials against legacy.

SL-19564 Rebalance exposure and sky.  Hack legacy diffuse map saturation and brightness to allow ACES Hill all the time.

SL-19538 Back off on sun brightening a bit, remove errant brightening of clouds, and update midday to not be red shifted.

* SL-19538 Remove hacky ambiance scale and take the mittens off probe ambiance values.  Fix for sky brightening being done in sRGB space.

DRTVWR-559 Dynamic exposure followup -- stochastic sampling, weight based on luminance and distance to center of screen, rebalance night, don't rely on blending not clamping R16F.

SL-19281 Unify handling of haze and gamma between fullbright and not and move haze back to sRGB color space to stay consistent with sky colors.  Also fix broken "roughness" stuck at 0.2.

SL-19015 Bump probe resolution back to 256 by default (drop to 128 if vram < 2GB), remove irradiance map feedback loop (one bounce, but but more stable and allows for much brighter first bounce), make sky contribution to irradiance not tint the world blue.  Make irradiance that appears in radiance maps match world irradiance.

SL-18190 Cleanup -- convert some vec4's to vec3's (as they really are), remove some unused glsl files.

SL-18239 Unify PBR and non-PBR treatment of ambient/SSAO/irradiance.  Restore SSAO to release version.

SL-18190 End of linear space odyssey -- just eat the conversions in atmosphericsFuncsF for sunlight and additive, but leave linear ambient in tact.

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.

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.

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.