Instead optimize based on the name feedback. This simplifies matters
for concurrent optimization.

Drive-by: Rename "index" to "key" for clarity where appropriate.

Bug: v8:7790
Change-Id: Id6db1174c7840c24044bc655e0ffee6a5b0de21c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1559742
Commit-Queue: Georg Neis <neis@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60709}