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

[Paul Heidekrüger via cfe-commits]

paulhdk wrote:

> LGTM for my changes, here a few nits that are just nice to have (doesn't much block PR). The only important change is [single ticks instead of double tick in default value of `ExcludeClasses` option](https://github.com/llvm/llvm-project/pull/95220#discussion_r2109589004).
> 
> P.S. Commented without official approval because I didn't have time to thoughtfully read all matchers and check code. Hope to do it in the future if there wouldn't be any feedback from previous reviewers.

Thank you for your quick reply and feedback, @vbvictor! I've incorporated all of the requested changes.

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