gltf exporter: new feature: export 'Loose Points' and 'Loose Edges'

io_scene_gltf2/__init__.py

io_scene_gltf2/blender/exp/gltf2_blender_extract.py

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

...cene_gltf2/io/exp/gltf2_io_draco_compression_extension.py