The actual fix is in LoadIC::ComputeHandler (checking
lookup_start_object == holder instead of receiver == holder) + the
LookupIterator changes for preserving lookup_start_object.

The rest is renaming / refactoring.

Bug: v8:9237, chromium:1127653
Change-Id: Ieef46fb46ababa79623951c48639429c5b552d2d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2414039
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70045}