[clang] [NFC][analyzer] Refactor switch handling in the engine (PR #178678)

[Balázs Benics via cfe-commits]

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

I welcome any changes that improve the readability of this part.
I read the patch but didn't really check if word-for-word this is NFC; and I don't think it's worth my time to tear this patch apart.

I trust you, if you say it's NFC, I'm practically good with any changes made here.

https://github.com/llvm/llvm-project/pull/178678