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

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timon-ul wrote:

> Based on the consistency claims made in the test comments, we'd still expect it to use void moon(int, int day);, right?

Well this is a surprise....so I guess the ordering of `redecls()` actually has some context to it and is not just in declaration order? Because I can replicate the exactly same in the AST test (if I add a 2nd parameter, if I stick with 1 it still passes). I will see if I can dig something up what is causing this, that being said AST and Index will still be consistent so while I am interested in why this happens I do not think it changes anything for this PR.

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