glTF exporter: perf: use numpy to speedup primitive extract

io_scene_gltf2/__init__.py

io_scene_gltf2/blender/exp/gltf2_blender_extract.py

io_scene_gltf2/blender/exp/gltf2_blender_gather_nodes.py

.../blender/exp/gltf2_blender_gather_primitive_attributes.py

...cene_gltf2/blender/exp/gltf2_blender_gather_primitives.py