Introduce plugin to enforce raw_span usage in fields

Bug: 329106310
Change-Id: I6c4a82259f7a1771d988ac90ca5c932b5fe1edb7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5379300


Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Ali Hijazi <ahijazi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283140}