Code ranges are currently accessed from outside the heap via an
internal structure of the heap.  This change lifts the accessor
function a level higher.  This should have no cost, but will
maintain abstraction better and allow the TPH interface to work
more readily.

Bug: v8:9533
Change-Id: I154d93ce46f5137b3e3b7ecc6bed7e5b8b0343a6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2039351Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Steve Blackburn <steveblackburn@google.com>
Cr-Commit-Position: refs/heads/master@{#66152}