[analyzer] pr47037: CastValueChecker: Support for the new variadic isa<>.

llvm::isa<>() and llvm::isa_and_not_null<>() template functions recently became
variadic. Unfortunately this causes crashes in case of isa_and_not_null<>()
and incorrect behavior in isa<>(). This patch fixes this issue.

Differential Revision: https://reviews.llvm.org/D85728