This CL updates DetachableVector to store the data at a known place
instead of in an std::vector<>, so that builtins can update it directly.

Bug: v8:8124
Change-Id: Iba5fb2e9d4e0ddc689d0f7eeaea40bc3218edf3a
Reviewed-on: https://chromium-review.googlesource.com/c/1297783
Commit-Queue: Taiju Tsuiki <tzik@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57452}