IsPendingAllocation will now load the space from the object's page
header first and then only check the object against the current LAB
of that particular space. Previously we were looking up that object
in the LABs of all spaces.

This new design also makes it feasible to have one dedicated mutex for
original_top/original_limit (respectively pending_object) for each
space. This will reduce contention on the mutexes.

Change-Id: I8e7636410259fd03b7970084bfbbaeadb2d8ba61
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2936606
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75054}