[compiler] Perform GetFieldIndexFor concurrently through Refs

Bug: v8:7790
Change-Id: I8ff80b109381b339864879e8e4e0dc0d5e418262
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2682636


Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73074}