Add a mechanism similar to the optimizing compile dispatcher, for tests
to be able to wait for Maglev compilation to finish, and to force
finalization.

Bug: v8:7700
Change-Id: I0ef542001fe9f6622b1231eb9406130ad81c8f6e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3865551
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Linke <jgruber@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82899}