Spawn primitives with physics from scripts

[saori-eth]

WIP implementation for spawning primitives with physics through scripts for generative content.

Current bugs:

• sometimes the material takes a second to load
• if i spawn around 5k rigidbodies at once i get memory overload. if i reduce it a bit, it lags but then runs max fps when they spawn

The AI went too far with the docs, this is just an example

[ashconnell]

I have a feeling it would feel less hacky if there was just a prim node that did both the collision and mesh together in one.
Then app code would simply be:

const box = app.create('prim', { 
  kind: 'box', 
  size: [1, 1, 1], 
  color: 'blue', 
  rigidbody: 'static' 
})
app.add(box)

And that would create both the mesh and the collider behind it.
Everything would be completely isolated inside one single nodes/Prim.js file