This fixes data races when lazily creating counters (and populating the
{counter_map_}, and when concurrently adding samples to the counters.
It also ensures that the Wasm engine is stopped (via {V8::Dispose})
before printing and deleting counters, as background threads might still
try to update the counters otherwise.

R=mlippautz@chromium.org
CC=​nikolaos@chromium.org

Bug: v8:12453, chromium:1275117
Change-Id: Ie6beea6cc74eea52143d12f9921597da4a250f2a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3308710Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78191}