Create ServiceWorker lib

[saschanaz]

Service workers basically extends from general worker but has their own types e.g. Client, ExtendableEvent, FetchEvent, etc. Will you accept a PR for this?

[mhegazy]

Yes, see microsoft/TypeScript#11781 and microsoft/TypeScript#14877

[13rac1]

A related issue for others who find this issue: Service Worker types were added by @saschanaz in #439

[saschanaz]

#1034

@github-actions close

[github-actions]

Closing because @saschanaz is one of the code-owners of this repository.