[clang-tools-extra] [clang-tidy] support string::contains (PR #110351)

[Nicolas van Kempen via cfe-commits]

https://github.com/nicovank commented:

IMO no need to update release notes:

> Improved `readability-container-contains` check to let it work on any class that has a contains method.

But I think an example should be added to [the check documentation](https://github.com/llvm/llvm-project/blob/6022a3a05f951632022c84416209fe6d70d9105c/clang-tools-extra/docs/clang-tidy/checks/readability/container-contains.rst).

https://github.com/llvm/llvm-project/pull/110351