Ref T6367. This is similar to D11329, but not quite as ambitious.
Allow Editors to implement supportsWorkers() and move their publishing work into a daemon. So far, only Paste supports this.
Most of the complexity here is saving and restoring state across the barrier between the web process and the worker process, but I think this is ~90% of it and then we'll pick up a couple of random things in applications.
I'm primarily trying to keep this as gradual as possible.