Port the CompilerDispatcher to use the Jobs API, instead of its own
hand-rolled worker management.

This required some re-thinking of how testing is handled, since the
tests want to be able to

  a) Defer calls to PostTask/Job, to actuall post the jobs later. This
     was easy enough with PostTask, since we could simply store the task
     in a list and no-op, but PostJob has to return a JobHandle. The
     tests now have a DelayedJobHandleWrapper, which defers all method
     calls on itself, and because of all the unique_ptrs, there's also
     now a SharedJobHandleWrapper.

  b) Wait until tasks/jobs complete. Returning from a Task meant that
     the task had completed, but this isn't necessarily the case with
     JobTasks; e.g. a job might be asked to yield. This patch hacks
     around this by Posting and Joining a non-owning copy of the
     requested JobTask, and then re-posting it once Join returns.

Change-Id: If867b4122af52758ffabcfb78a6701f0f95d896d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2563664
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77618}