SL-20606: Reuse vertex buffer between preview renders. Fix preview sometimes zoomed in too much. Miscellaneous cleanup

SL-20611 Followup -- fix for depth based atmospheric mask making atmospherics effect sun/moon/clouds

This commit fixes a bug introduced with commit 6472b75b
where the fullbrightF.glsl shader fails to set color.a to final_alpha for HUDs.

SL-20611 Followup -- fix for artifacts on water surface from GPUs that don't like to read from a depth buffer that is bound for writing

SL-20654 Fix for box probes sometimes glitching out at the corners.  Incidental fix for crash when mWaterPool is null.

SL-20611 Followup -- fix edge cases with transparent PBR objects around eye/object above/below water.

SL-20611 Make haze effect local lights -- move sky and water haze to their own passes and unify sky and water haze in forward rendering shaders.

SL-20440 Fix for projector ambiance destroying PBR shading.  Also fix longstanding bug with hard line in projector ambiance lighting.  Incidental decruft of legacy_adjust and LOCAL_LIGHT_KILL, etc.

Enforce a minimum roughness to 0.045 in PBR shaders to avoid div by zero and for consistency with Substance and UE/Unity