[clang] [Clang][RAV] Simplify TraverseTemplateArgumentLocsHelper (PR #199131)

[Harald van Dijk via cfe-commits]

hvdijk wrote:

It's annoying and disrespectful that people involved this PR would then submit a later conflicting PR, fixing the bugs that this was meant to fix, without commenting here, and without including the tests to ensure that this remains fixed.

I've updated this PR to resolve the conflicts and keep the simplification and tests. Please let me now just actually merge it.

https://github.com/llvm/llvm-project/pull/199131