Add a box shape to this body.
Center of the box, relative to PhysicsBody.Position of this body.
Rotation of the box, relative to PhysicsBody.Rotation of this body.
The extents of the box. The box will extend from its center by this much in both negative and positive directions of each axis.
Whether the mass should be recalculated after adding the shape.
The newly created shape, or null on failure.