Configure script's settings and realm for service workers
Service workers have a different script execution model from other
workers. Update algorithm fetches a service worker script, and Run
Service Worker algorithm runs the script when installing it and whenever
functional events and message events need to be dispatched.
This change:
- Passes null as the value of script settings object/module map
settings object argument to fetch a classic worker script/fetch a
module worker script graph algorithm, respectively, called in Update
algorithm, instead of the placeholder argument "the to-be-created
environment settings object".
- Sets the script's settings to the environment settings object created
in Run Service Worker algorithm and the script's record.[[Realm]] to
that settings object's Realm.
Fixes #1013.
