Rather than requiring the user of a LocalIsolate to pass in a
RuntimeCallStats from a WorkerThreadRuntimeCallStatsScope, create the
scope in the LocalIsolate directly and use its RuntimeCallStats in the
LocalIsolate constructor.

We can't do this for the main thread LocalIsolate, since
WorkerThreadRuntimeCallStatsScope doesn't work on the main thread, so
there we use the main-thread RuntimeCallStats instead.

This flushes out some issues of background-thread LocalIsolates being
used on the main thread, so fix those too, as well as RCS scopes using
background counters for operations that could happen on the main thread.

Change-Id: I21a53be0771f47a03ccdb27d24c2b9d25d8b2d1c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3318664Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78334}