... when deserializing.

EphemeronHashTables require valid HeapObject keys, however
EphemeronHashTables are filled with Smi::uninitialized_deserialization_value
when deserializing. We could fill EphemeronHashTable's elements
with "the initial filler" which is undefined value to make sure
the elements are valid.

Bug: v8:13232
Change-Id: I268cdbd4303fbe9afa2f9a5d8aafcace397c8164
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3864185
Commit-Queue: 王澳 <wangao.james@bytedance.com>
Reviewed-by: Jakob Linke <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82808}