Fixes#15474.
Notes:
* page-level requests that are also handled by a SW's fetch handler, should not be interceptable at the page-level
* `Network.requestWillBeSent` does not provide enough metadata for Playwright to fire the `request` event at that time, so it does it as soon as it gets to the end of the request lifecycle
The Service Worker tests had some races in them that only were apparent
on the bots. To repro, I ran the tests with:
```
xvfb-run taskset -c 0 npm run ctest -- chromium.spec.ts --headed --reporter=line --repeat-each 10 --workers=1
```
Just because Playwright has a SW, does not mean the worker has fully loaded
it's main/import scripts.
