SL-20553: Fix crash in ~PBRPickerAgentListener

* SL-20570 Fix for lossy (and square) normal maps when importing GLTF materials.

* SL-20582 Fix for overriding to alpha mode blend not working.  Incidental decruft of dead code (thanks, Rye!)

SL-20553: Save material button in build floater now depends on agent inventory rather than object inventory

SL-20553: Save material button in build floater now depends on agent inventory rather than object inventory

SL-20582 Fix for overriding to alpha mode blend not working.  Incidental decruft of dead code (thanks, Rye!)

also added suggested continue statements, and removed obsolete
LLInventoryItem::fromLLSD deserialization codepath.

Update editor in which texture changed to local

ensure inventory skeleton loading doesn't block the message system from processing packets.

SL-19979 Fix for frame stalls on mac with shadows enabled.  Also fix multihreaded GL not working on mac (thanks, Rye!)

SL-20397: Fix material set from script not updating when the GLTF material has non-default texture transforms