SL-17074 Redo ALT-F4 handling fix

Merged previewAvatar and generateImpostor into a single function since they are nearly identical

SL-17000 improve error message for physics mesh import

SL-17077 Ensure profiling is disabled if gpu_benchmark fails.  Log the source of the real crash for when the viewer inevitably crashes later.

SL-16993

Approved-by: Euclid Linden

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

SL-17074 Fix Alt-F4 handling bug

Might be a better idea to turn LLWorld back into an LLSingleton. Too many things to track.

When animesh stops being an animesh it might still be in a list, but will no longer have an avatar

SL-17005 WIP Simplify what feeds texture loading bias to only pay attention to available memory according to OS and GL driver, not (broken) internal accounting (breaks intel GPUs, compatibility pass incoming).

More DRTVWR-550 Teamcity build fix. another piece of python2 syntax leftover in an error handling block