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.

SL-19713 Fix for broken avatar preview render in animation upload.  Incidental decruft and camera FoV network spam reduction.

* Fix water fog mismatch between alpha blend and opaque when local light is nearby

* Add PBR underwater alpha blend shader

DRTVWR-559 Remove RenderReflectionProbeCount (which is bugged) and lean on RenderReflectionProbeLevel for preferences (which works).

DRTVWR-583
DRTVWR-559

DRTVWR-583

SL-19709 Fix for fullbright shiny not factoring out exposure and flickering fullbright alpha.  Incidental decruft.

DRTVWR-583

DRTVWR-559 Add "No Post" mode and refactor "Scene Gamma" into "Brightness" for adjusting legacy gamma when probe ambiance is 0 and dynamic exposure when probe ambiance is not zero.

SL-19560 Revert hacky fix for other avatars having low res BoM textures.  Fix for brightening of PBR materials at the shadow horizon.

DRTVWR-559 Add control for automatic reflection probes to advanced preferences and featuretable. Remove Reflections checkbox.  Don't persist reflection probe volume display between sessions.  Incidental decruft.

TODO: Why did this work for the equivalent non-rigged prim?

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

DRTVWR-583

DRTVWR-559
SL-19524
SL-19513

SL-19569 Don't reset probes when crossing parcel borders (whoops) and tone down glare on legacy materials.

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

Makes our binding flow _far more_ predictable and makes way more sense.

DRTVWR-559
SL-19524
SL-19513

SL-19538 Remove clouds from irradiance maps and don't conflate max probe samples with max probe neighbors, and don't move manual probes after they are complete (removes flickering around Sponza).

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

SL-19538 Followup -- scrub all possible sources of NaNs, make dynamic exposure controls not persist, limit exposure range, and do a debug gl pass.

* SL-19538 Followup -- fix for dynamic exposure having large gaps in its luminance sampling.

* SL-19538 Followup -- review feedback changes.

SL-19538 Followup -- tune exposure parameters and clamp local light ambiance.  Make render targets 16F and scrube NaNs (thanks Rye).  Update midday. (#154)