This fixes places that assume that DescriptorArray is a WeakFixedArray.

In addition to the existing:
 - LoadDetailsByKeyIndex
 - LoadValueByKeyIndex
 - LoadFieldTypeByKeyIndex
This introduces Load*ByDescriptorEntry versions and LoadKeyByKeyIndex.

Bug: v8:8486
Change-Id: I958867138df7756c715ae3d449b3206a32076514
Reviewed-on: https://chromium-review.googlesource.com/c/1346501
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57727}