Naming conventions around "TypeScriptWorker"

As discussed under the [PR for refactoring the Language Service](https://github.com/google/playground-elements/pull/211), we should move into calling the current "TypeScriptWorker" in a more general name as just a "WebWorker" or something similiar.

Some pointers from the PR to keep in mind:

- Rename the `typescript-worker` -directory to just `web-worker`
- Change the build output in RollUp to match (`playground-typescript-worker.js` => `playground-web-worker.js` )
- Change the worker file references in `playground-project.ts`
- Change the variable naming to remove typescript from it.

With these changes, we are creating a breaking change as the build output names change as informed by @aomarks [here](https://github.com/google/playground-elements/pull/211#issuecomment-927148690).

Creating a issue so that the needed steps can be documented before we decide to ship the changes