This complements [Shared]ArrayBuffer::GetBackingStore and allows the
embedder to transfer (shared) array buffers using only BackingStores.

Bug: v8:9380
Change-Id: I4714a27e06d5be43aef06dc633f11f2d43e4ee75
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1811037
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63889}