All preRebuild crashes appear to be LLVolumeImplFlexible

According to bugsplat's "Locals", viewer tried to iterate through 536018048 faces
LLVolume pointer seemed to be valid but data in LLVolume wasn't, so likely vobj was invalid

By the time this will release, enough time should have passed for smooth transition.
Alternative to removing this is to make it check build id for anything older than 6.4.17.557391

Contribution by Rohacan Hirons

SL-14717 Follow ups

SL-14717 Using the cached setting in LLToolPie::handleHover()

getItemIndex() on each insertion can be very expensive, use std::set's find instead

Don't resort whole branch of inventory if created(loaded) item is not newer. Should also stabilize fetch phase a bit.

following promotion of DRTVWR-514

This reverts commit a106d6cf.

This particular case of LLAPRFile crashes due to thread issues (and if it doesn't it might be affecting some other apr call due to using default pool).
Function is not opening the .dsf file in question and LLAPRFile won't ensure that file exists till the end of the function, it just checks that file exists at a given moment. No point to overcomplicate things by adding thread safe pool, so replaced with dirutil.

# Conflicts:
#	indra/newview/llviewerstats.cpp

SL-14862 - use nested LLSD for widget info, condensed to the two leaf-most elements of the path. Simplified floater logging.

following promotion of DRTVWR-532

This reverts commit e61f485a, reversing
changes made to 00c47d07.

following promotion of DRTVWR-519