This CL makes {CompilationState::WaitForTopTierFinished} reuse the logic
in {CompilationStateImpl::WaitForCompilationEvent}. In order to support
that new use case better, the latter is improved by
1. stopping compilation (in that one thread) as soon as the event has
   been seen, and
2. also executing top-tier units if needed.

R=ahaas@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_isolates_rel_ng
Change-Id: Ia20f54c195ba8670b10fc6790db28af04e8f40b0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2637862
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72200}