* split ops/worker.rs into ops/worker_host.rs and ops/web_worker.rs
* refactor js/workers.ts and factor out js/worker_main.ts - entry point for WebWorker runtime
* BREAKING CHANGE: remove support for blob: URL in Worker
* BREAKING CHANGE: remove Deno namespace support and noDenoNamespace option in Worker constructor
* introduce WebWorker struct which is a stripped down version of cli::Worker