For measuring the time spent in each phase of TurboFan we use
PipelineRunScope that adds a RuntimeCallStats scope with the correct counter.
PipelineRunScope uses the runtimestats table set on the PipelineData to
initialize the RuntimeCallStats scope. We correctly set the runtimestats on
the pipelineData when starting ExecuteJobs but don't set it on PrepareJobs.
This cl fixes it to also set runtimestats table on PrepareJobs. PrepareJobs
always run on main thread, so it should be safe to use the runtimestats table
on the isolate.

Change-Id: Ied211158a10197aabb94373967146089a48c2db0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1995386
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65737}