Move index constants into the wrapper, add getters, and use the
wrapper in more spots.

Bug: v8:1166136
Change-Id: I3f37a541482fd6b7c604719c759952a72d58bad2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2637218
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72198}