[clang] [clang-tools-extra] [clangd] CodeCompletion surface param names if possible (PR #206716)

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timon-ul wrote:

I realise, maybe I did not explain the current behaviour of iterating over the recelarations properly. I think the link the  [Redeclarable.h](https://searchfox.org/llvm/source/clang/include/clang/AST/Redeclarable.h#32) really explains it well, but basically they are on a circular linked list that links backwards and they just walk that one from the current one until it reaches itself again.

https://github.com/llvm/llvm-project/pull/206716