Merge GLTF PBR Maint 2 to main.

.github/workflows/build.yaml

autobuild.xml

doc/testplans/optimize_away_alpha.md

indra/llcommon/indra_constants.cpp

indra/llcommon/indra_constants.h

indra/llcommon/llcoros.cpp

indra/llcommon/llerror.cpp

indra/llcommon/llerror.h

indra/llcommon/llexception.cpp

indra/llcommon/llsingleton.h

indra/llcorehttp/_httpservice.cpp

indra/llimage/llimagebmp.cpp

indra/llimage/llimagedxt.cpp

indra/llimage/llimagetga.cpp

indra/llrender/llimagegl.cpp

indra/llrender/llrender.cpp

indra/llrender/llrender.h

indra/llrender/llrendernavprim.cpp

indra/llui/llnotifications.cpp

indra/llui/lltexteditor.cpp