Support URL tunnelling (pass dwds UrlEncoder through to editors via daemon) (#44271)

* Prposal for supporting URL tunnelling

* Update daemon.md

* Add the ability for daemon to call clients to expose URLs

* Fix dwds mock in web_fs tests

* Fix type error

* Remove build_runner import from run

* Move appStartedTime back to after the app has started

* Remove nested DI scope and pass urlTunneller down

* Fix import

* Tweak TODO

* Fix existing tests

* Fix spec to use result instead of params for response object

* Fix exposeUrl to use a url field, as spec'd

* Test that the daemon's exposeUrl sends a request and handles the response