If we insert a second SIMPLE_PROPERTY_ARRAY we move from kWeakRef
encoding to kFullTransitionArray encoding. As always, we are searching
in the meantime in a background thread.

Bug: v8:7790
Change-Id: I5e3d85657dda4c199e50b9c35e7f617f1821a8f0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2243218Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68980}