[llvm] [IR] Avoid visited set for simple isScalableTy queries (NFC) (PR #221743)

[Alexis Engelke via llvm-commits]

aengelke wrote:

Might be even better to store properties like this in the Type on construction/setBody and have isScalableTy&friends just return that bit? We don't have that many types, so even growing Type should be ok.

https://github.com/llvm/llvm-project/pull/221743