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

Put 2k textures behind a feature flag

https://github.com/secondlife/viewer-issues/issues/21 Just use existing settings to block uploads larger than 1024.

* SL-20760 Allow 2k texture uploads

* SL-20760 Fix for textures not downloading.

Co-authored-by: RunitaiLinden <davep@lindenlab.com>

And hide warning when it's already 0

SL-19555 Fix picker failing to highlight default material in inventory

following promotion of DRTVWR-596

SL-20754 Modify default midday to be a better approximation of Cloud Layers HDRI (addresses blue sheen).

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

following promotion of DRTVWR-587