This reverts commit 3df36990.

Reason for revert: Breaks MSVC bot (https://cr-buildbucket.appspot.com/build/8880517266974148704)

Original change's description:
> cppgc: Port ObjectStartBitmap
> 
> This ports ObjectStartBitmap from Blink.
> 
> Bug: chromium:1056170
> Change-Id: Ib959d9ac1c5e1e34ffa6418f77956e993c570ffc
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2181331
> Commit-Queue: Anton Bikineev <bikineev@chromium.org>
> Reviewed-by: Omer Katz <omerkatz@chromium.org>
> Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67735}

TBR=ulan@chromium.org,mlippautz@chromium.org,bikineev@chromium.org,omerkatz@chromium.org

Change-Id: Iaea15b11c0ee7b599fe1f275aded7414bce428ac
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:1056170
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2196321Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67742}