[clang] [alpha.webkit.UncountedCallArgsChecker] Fix a false negative when a call argument is a local variable. (PR #129974)

[Ryosuke Niwa via cfe-commits]

rniwa wrote:

On hindsight, the existing code is correct. We're lying on local variable checker to check the liveness of a local variable. Call arguments checker was just relying on that.

https://github.com/llvm/llvm-project/pull/129974