This CL make TPH be able to access some heap private interfaces, by
marking TPH classes as friend classes.

Bug: v8:11641
Change-Id: I72aebf267c8f36593f50279bec5dccb44cda9528
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2994220
Auto-Submit: Wenyu Zhao <wenyu.zhao@anu.edu.au>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Commit-Queue: Wenyu Zhao <wenyu.zhao@anu.edu.au>
Cr-Commit-Position: refs/heads/master@{#75572}