[api] Replace a few auto's

Change-Id: I4c2347e9b75ef36c37b46d527ad6c4338dc20819
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3162047


Reviewed-by: Patrick Thier <pthier@chromium.org>
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76863}