[clang] [clang-tools-extra] [clang-tidy] Add new check: `readability-redundant-typename` (PR #161574)

[Victor Chernyakin via cfe-commits]

localspook wrote:

[Ran the check over libc++ in C++20](https://github.com/llvm/llvm-project/commit/1e83e4755ccfc3657cb19c67db5df50e21522cd9), and it found one false negative and one quite significant false positive (in template instantiations).

https://github.com/llvm/llvm-project/pull/161574