Service Worker API in Dedicated Worker WebIDL changes

This change in a series of changes to support Service Worker APIs in
Dedicated Workers. See https://crbug.com/40364838

This modifies the WebIDL to expose navigator.serviceWorker in the
Dedicated Worker global context and using the
ServiceWorkerInDedicatedWorker feature flag.

Bug: 40364838
Change-Id: I85cbc85fa3fd4602e6bd9c44c96fba3b1132cf54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6639507
Commit-Queue: Dave Risney <david.risney@microsoft.com>
Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1479944}