Eventually this should be used to prevent OS stack overflow
on background threads.

Drive-by change: make more things const.

Bug: v8:10974
Change-Id: Ie659e53992f58c7c08920985d54175d61c5ee796
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2474117Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Dominik Inführ <dinfuehr@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70650}