SL-19394: Change default midday to an asset ID with probe ambiance

Phase 2 of work on SL-18458 material override cache fixes

DRTVWR-559 Quality pass -- Fix sky banding, fix off-by-one-mip in reflection probes (thanks Rye), remove noiseMap from light shaders (removes speckles), make irradiance maps RGB16F instead of RGBA16.  Use actual luminance for sky instead of max color component during irradiance map pass.

SL-19434: Fix texture issues with minimap, but keep performance from SL-19331

This reverts commit 084ef517.

SL-19331: Improve performance of setSubImage (ex: media updates)

Partial solution for SL-18458 Materials override cache not working and related SL-18684/SL-19206/SL-19173

SL-19389: Fix textures not being optimally loaded after the fix in SL-19338

In the future, some uses of glTexSubImage2D should be better vetted, ex: media prims

SL-19330: Fix texture animation in wrong direction when setting material on another side

Sl 19338: Fix textures not loading when RenderCompressTextures is 1