- Adds regular native heap entries to the HeapObjectsMap.
- Adds a side map for keeping a mapping of native objects to their canonical
  heap entry that they have been merged into.

Change-Id: Ida00628126ded1948ceb2a0cbe14da817af7f361
Bug: chromium:988350
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1720810
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63140}