Ban raw_ptr<T>::operator[] under enable_pointer_arithmetic_trait_check.

Treat operator[] the same as, say, operator+= when the specific
BUILDFLAG is set.

-- fix instances thus uncovered.

Change-Id: Ic436875af87b0ca922b5e344753cc8a6acee4aa5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4834929
Owners-Override: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Bartek Nowierski <bartekn@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1198100}
NOKEYCHECK=True
GitOrigin-RevId: d83ed1b22705801b8e6d171a46735034430ec420