Create a static version of Heap::CreateFillerObjectAt which can't clear
slots (as it doesn't access the heap), but can therefore be used in the
OffThreadHeap. This will allow off-thread deserialization in the future.

Bug: chromium:1075999
Change-Id: I4b4046ccfaa51822350ff7c384dbe33e621ed4f5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2170230
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67528}