Creates new APIs to get Shared Memory statistics like the size of
read-only space and potentially the memory used by shared array buffers.

Currently all shared memory statistics are zero.

Bug: v8:7464
Change-Id: Ib8d58f885beaa1d65ccef7b64dd4f3db4149bca3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1900465
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64831}