This avoids the {StatsCounter::lookup_done_} field by always
initializing the {StatsCounter::ptr_} field in {StatsCounter::GetPtr()}.
This makes the fast path for updating the counter value much simpler and
faster.

R=mlippautz@chromium.org

Bug: v8:12482
Change-Id: I89d094b15e0417bbfb302006de8eede0c200202d
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_linux64_ubsan_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3322768Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78314}