With this CL, blocks at the end of the ExternalPointerTable that are
completely empty after sweeping will be decommitted to reduce the
table's memory footprint.

Bug: v8:10391
Change-Id: I1002e95a0f9c22400fdd2620047d86738a1f7af4
Cq-Include-Trybots: luci.v8.try:v8_linux64_heap_sandbox_dbg_ng,v8_linux_arm64_sim_heap_sandbox_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3791903Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Samuel Groß <saelo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82085}