Remove the concept of JobId from LazyCompileDispatcher, and make SFIs
the canonical id for these jobs.

This has several consequences:

  * We no longer split enqueing a job and registering a SFI with that
    job. We did this previously because we could not allocate SFIs in
    the Parser -- now with LocalHeap we can, so we do.
  * We remove the separate Job vector, and make the SFI IdentityMap
    hold pointers to Jobs directly. This requires a small amount of
    extra care to deallocate Jobs when removing them from the map,
    but it means not having to allocate new global handles for jobs.
  * The SFI is passed into the BackgroundCompileTask instead of the
    script, so our task finalization doesn't need the SFI anymore.
  * We no longer need to iterate ParallelTasks after compiling (to
    register SFIs), so we can get rid of ParallelTasks entirely and
    access the dispatcher directly from the parser.

There are a few drive-bys since we're touching this code:

  * Jobs are move to have a "state" variable rather than a collection
    of bools, for stricter DCHECKing.
  * There's no longer a set of "currently running" jobs, since this
    was only used to check if a job is running, we can instead inspect
    the job's state directly.
  * s/LazyCompilerDispatcher/LazyCompileDispatcher/g

Change-Id: I85e4bd6db108f5e8e7fe2e919c548ce45796dd50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3259647
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77712}