Inline "finalize and report timing"

As long as fetch callers pass in the necessary data through the request concept, they will not have to make additional calls to get timing reported accurately. Note that this does not work if callers want to use useParallelQueue.

Downstream PRs:
* whatwg/html#7722
* whatwg/xhr#347
* w3c/csswg-drafts#7355
* w3c/beacon#75
* w3c/resource-timing#321
* https://github.com/w3c/navigation-timing/pull/1760

Closes #1208 and closes w3c/navigation-timing#131.