[clang] [clang-tools-extra] [NFC] Add implicit cast kinds for function pointer conversions (PR #110048)

[Akira Hatanaka via cfe-commits]

ahatanak wrote:

This change isn't needed anymore as it was decided that noexcept shouldn't be used to compute discriminators of function and member function pointers (see https://github.com/llvm/llvm-project/issues/106487#issuecomment-2440364300).

https://github.com/llvm/llvm-project/pull/110048