Web Replay: simulate network callbacks directly by calling ResourceLoader.

We still capture network callbacks using ResourceHandle shims, but on
replay we simulate the callbacks by digging a ResourceLoader out of
the active document loader and calling the correct callback. This
removes handle ids from callback input subclasses and adds a frameIndex.
Web Replay: remove NetworkProxy handle map, consolidate callback classes.

ResourceHandles are no longer stored or used during replay.

Variants of ResourceDidFail were folded into one class. The memoized
ResourceLoaderDestroyed was removed, since it never worked anyway.

Remove callbacks from Capturing ResourceHandleClient that don't implement
any capturing functionality.
Web Replay: don't let ResourceLoaders load during replay.

Also, don't make dummy ResourceHandles and clients.