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

[Paul Heidekrüger via cfe-commits]

PBHDK wrote:

> Btw, I realize that this check is part of the [bounds profile](https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#SS-bounds) (Bounds.4), so for consistency it should probably be named `cppcoreguidelines-pro-bounds-...`.

What do you think of: `cppcoreguidelines-pro-bounds-avoid-unchecked-container-accesses`?
That's just me attempting to capture all of the previous suggestions in one name.

> This becomes then the last remaining check to complete the bounds profile!

That was actually @leunam99's and my main our motivation for getting involved with this work :-)

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