Migrate wrapper compilation from the tasks API to the job API. This
avoids querying the platform for the number of available threads, and
makes the code much more idiomatic.

R=thibaudm@chromium.org
CC=etiennep@chromium.org

Bug: chromium:1101340
Change-Id: I2d84176fe729c065348fd479fe8fd1a0d2f19a50
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2471379
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70620}