SL-17194 Impostor quality pass 2 (and fix for fully transparent rigged attachments rendering to depth buffer)

SL-17028 Fix for inconsistent ordering of transparent rigged meshes and removal of glow-only rigged meshes from depth buffer.

SL-16468 Fix for crash when enabling highlight transparent (add rigged mesh support to highlight transparent).

SL-14732: Merge Sovereign Engineer's cloud patch: Fix writing outside outside of the bound fbo in forward render class2 cloud shader

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

Contribution

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.