This removes another liability of the finisher: to abort compilation
and publish errors once an error state has been set by a background
compile unit.
This CL makes background threads set the error state directly and
schedule a foreground task to actually publish the error (e.g. via the
promise).

R=mstarzinger@chromium.org

Bug: v8:7921
Change-Id: I7a6a7ca4f235c2ad374b6ffc434eb6ac7d5f54ae
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/1307425Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57135}