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: If6e06ea8621fd6aff374c04247c3168b2cbb361a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1568712Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Yu Yin <xwafish@gmail.com>
Cr-Commit-Position: refs/heads/master@{#60912}