debug helper: draw shapes of physics objects

[hannojg]

It would be helpful to see the shapes we create in the physics world during development.

I think the simplest implementation would be to just draw boxes. We could create aabb for the bullet shapes and then use:

https://github.com/google/filament/blob/93b15dac87d255ac6c6b66ddaf9aa00ea5a55a3f/samples/lightbulb.cpp#L363-L367

Otherwise we could just render all vertices:

https://github.com/google/filament/blob/93b15dac87d255ac6c6b66ddaf9aa00ea5a55a3f/samples/hellotriangle.cpp#L133-L159

(The downside to that seems to be that we need to have some kind of material)

[hannojg]