feat(2d): add camera node

[ksassnowski]

This PR adds an orthographic camera node.

There a still a few kinks that I'd like to work out before merging this:

• The hit method selects the correct object, but the actual overlay in the editor is offset. I'm not sure why this happens.
• I would like most of the camera's methods to return a SignalGenerator in order to be chainable. I'm not sure what the best way to do this would be, however.

[aarthificial]

We could probably make the scene accept any ComponentChildren including a fragment (<>) by specifying a parser for the signal like this:

@parser((children: ComponentChildren) => {
  if (children instanceof Node) {
    return children;
  } else {
    return new Node({children});
  }
})
@signal()
public declare readonly scene: Signal<ComponentChildren, Node, this>;