[clang-tools-extra] Enforce SL.con.3: Add check to replace operator[] with at() [Cont.] (PR #95220)

[Paul Heidekrüger via cfe-commits]

PBHDK wrote:

> The name sounds nice. Thanks.
> Please address the concerns here and in #90043 to always suggest `at` as well. An option to enable suggesting and providing a fix to use `at` (or `gsl::at`), like others have suggested, sounds like the best option.

Thank you for taking another look as well as your comments. On it!

https://github.com/llvm/llvm-project/pull/95220