port https://crrev.com/c/1541476

Original Commit Message:

     This CL adds handling for cleaning up weakmap (EphemeronHashTable)
     keys during scavenge, even if the weakmap resides in oldspace.

Change-Id: If0598a499641ba502b00857204e32ca63e0712c3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1564320Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Yu Yin <xwafish@gmail.com>
Cr-Commit-Position: refs/heads/master@{#60837}