[Verifier] Verify scoped noalias metadata

Verify that !noalias, !alias.scope and llvm.experimental.noalias.scope
arguments have the format specified in
https://llvm.org/docs/LangRef.html#noalias-and-alias-scope-metadata.
I've fixed up a lot of broken metadata used by tests in advance.
Especially using a scope instead of the expected scope list is a
commonly made mistake.

Differential Revision: https://reviews.llvm.org/D110026