Fix glb-parser normals generation (#2276)
Fix glb-parser normals generation (#2276)

* cleanup and fix normal generation
* add comment
* add correctness check
MicroWorldwide/PlayCanvas,aidinabedi/playcanvas-engine,sereepap2029/playcanvas,MicroWorldwide/PlayCanvas,sereepap2029/playcanvas,playcanvas/engine,aidinabedi/playcanvas-engine,sereepap2029/playcanvas,playcanvas/engine