Megamorphic load builtins are a performance optimization when current
feedback is megamorphic. We can't make this assumption for shared NCI
code though, since feedback in other native contexts may *not* be
megamorphic, and we'd thus miss out on necessary feedback collection.

Bug: v8:8888
Change-Id: I2adc5ef9a6b021b35cf26f975c79228d556bf94f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2546694
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71264}