During ExternalPointerTable::Grow, if we cross one of a handful of
predefined utilization thresholds, we now request a (major) GC to free
up entries that are no longer used in the table.

Bug: v8:10391
Change-Id: Id2d262f0f1d4dc37aec1e4978a8be2d223fb2b2b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3890971
Commit-Queue: Samuel Groß <saelo@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83155}