[clang] [clang-tools-extra] [clang] NFC: change more places to use Type::getAsTagDecl and friends (PR #155313)

[Shafik Yaghmour via cfe-commits]

shafik wrote:

I am not sure it makes sense to label such larger changes NFC, anything this large should have at least one review if not more.

https://github.com/llvm/llvm-project/pull/155313