Support Object3d

[alexpineda]

hey there,

this looks like an interesting library and I wouldn't mind trying it out. There does seem to be a problem for me in that I'd like to use regular old Object3D. Am I correct that without enabling options faces or vertices that geometry is only required for the boundingSphere? I'm wondering maybe if there is a way to generalize that.

Use cases include:

• GLTF which have the scene (Group) as the root object
• Instancing where I could use an Object3d to represent an instance
• In the future when Object3D will have optional bounding volumes InstancedMesh: Add bounding volumes. mrdoob/three.js#21507