This is a reland of bc33f5ae

Original change's description:
> Reland "[arraybuffer] Rearchitect backing store ownership"
> 
> This is a reland of 31cd5d83
> 
> Original change's description:
> > [arraybuffer] Rearchitect backing store ownership
> > 
> > This CL completely rearchitects the ownership of array buffer backing stores,
> > consolidating ownership into a {BackingStore} C++ object that is tracked
> > throughout V8 using unique_ptr and shared_ptr where appropriate.
> > 
> > Overall, lifetime management is simpler and more explicit. The numerous
> > ways that array buffers were initialized have been streamlined to one
> > Attach() method on JSArrayBuffer. The array buffer tracker in the
> > GC implementation now manages std::shared_ptr<BackingStore> pointers,
> > and the construction and destruction of the BackingStore object itself
> > handles the underlying page or embedder-allocated memory.
> > 
> > The embedder API remains unchanged for now. We use the
> > v8::ArrayBuffer::Contents struct to hide an additional shared_ptr to
> > keep the backing store alive properly, even in the case of aliases
> > from live heap objects. Thus the embedder has a lower chance of making
> > a mistake. Long-term, we should move the embedder to a model where they
> > manage backing stores using shared_ptr to an opaque backing store object.
> > 
> > R=mlippautz@chromium.org
> > BUG=v8:9380,v8:9221
> > 
> > Change-Id: I48fae5ac85dcf6172a83f252439e77e7c1a16ccd
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1584323
> > Commit-Queue: Ben Titzer <titzer@chromium.org>
> > Reviewed-by: Ben Titzer <titzer@chromium.org>
> > Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> > Reviewed-by: Yang Guo <yangguo@chromium.org>
> > Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> > Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> > Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#62572}
> 
> Bug: v8:9380, v8:9221
> Change-Id: If3f72967a8ebeb067c0edcfc16ed631e36829dbc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1691906
> Commit-Queue: Ben Titzer <titzer@chromium.org>
> Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#62809}

Bug: v8:9380, v8:9221
Change-Id: I9a2525753ae2424108d074fa81df5f25d945c824
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1709409
Commit-Queue: Ben Titzer <titzer@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62847}