assimporter fix issue AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS does not exist
requested to merge nmariusp/qtquick3d:work/nmariusp/AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS into kde/5.15
No matter if I use assimp from the Linux distribution or the one builtin to Qt5. These two symbols are not defined. So I have expanded the two macros. Based on the definitions in /home/n/kde/src/Qt5/qt3d/src/3rdparty/assimp/code/glTF2Asset.h:176.