[clang-tools-extra] [clang-tidy] Speed up `readability-container-contains` (PR #175121)

[Victor Chernyakin via cfe-commits]

localspook wrote:

> And the check doesn't work if we use actual map instead of fake one:

This seems to be because of the unfortunate fact that `std::map` only got a `contains` function in C++20:
https://en.cppreference.com/w/cpp/container/map/contains.html
https://godbolt.org/z/T7K4cY4ar

https://github.com/llvm/llvm-project/pull/175121