[clang-tools-extra] [clang-tidy] Update llvmlibc-implementation-in-namespace to new rules (PR #66504)

[Piotr Zegar via cfe-commits]

https://github.com/PiotrZSL approved this pull request.

As a single small change to make hardcoded namespaces configurable looks fine.
I added some comments related to overall issues in this check.
Fell free to fix them or ignore them.

https://github.com/llvm/llvm-project/pull/66504