Triangle-based worker communication for app => vdom => main => app

In case we render & mount a component or in case we do a vdom update, the worker messages are running like this: app => main => vdom => main => app

We can reduce this to: app => vdom => main => app

To do this, we need to create a new MessageChannel for the vdom worker, similar to the ones for the canvas and data workers. However, we only need to register one port (since messages back from vdom still need to drop the deltas inside main).

We still want to delay sending a reply from main to app until the deltas got processed by the renderAnimationFrame queue.