This CL only moves method definitions from heap.cc into the new file
heap-verifier.cc. Apart from this code is not changed.

Bug: v8:11708
Change-Id: Ice7e5f12c6370bc05b82b3a7bd15f94292c4235f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3856260Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82761}