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

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bgra8 wrote:

> > Could this information help you pin-point the issue, or a reproducer is necessary?
> 
> @bgra8 Thanks for the heads-up, a reproducer is always helpful, as we can include it in the test suite and make sure it never happens again. Since this involves modules, it probably wouldn't be simple to create a reproducer based on just those hints.

The reproducer will also be a huge amount of work as the target has a huge list of dependencies. I'll see what I get.

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