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

[Baranov Victor via cfe-commits]

vbvictor wrote:

And the check doesn't work if we use actual map instead of fake one:
https://godbolt.org/z/xxWdzGs9d

And If you instantiate the function, it works with the template.

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