[clang] [clang-tools-extra] [clangd] Fixed signature help for static call operator (C++23) (PR #199192)

[via cfe-commits]

Ippo47 wrote:

I looked at the code and i think the slicing only happens when FirstArgumentIsBase is true. When called from signature help, FirstArgumentIsBase is false so the object argument never gets removed for static candidates, the fix is also doing similar thing just externally by intercepting static candidates before they reached AddFunctionCandidates. But you are correct i will make changes in that portion ans revert my chnages. 

https://github.com/llvm/llvm-project/pull/199192