[clang] [clang-tools-extra] clangd: Extend reference search with constructor calls through forwarding (PR #169742)

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timon-ul wrote:

Even though you did not sound convinced to me, I decided to add a depth limit, because I rather have it fail on a certain depth then produce a stack overflow in weird edge cases. That being said, not sure if 10 is too much/too little, kinda guessing here which I also do not like, but I have no idea what to base this on.

Also while getting rid of unneccessarry `<vector>` includes I noticed quite a few unusued imports I then decided to also clean up, Not sure if I am overstepping here. Only `IndexingOptions.h` I did not dare to touch since that is outside of the clangd sphere and I do not know how much depends on it and what stuff I should compile to make sure.

https://github.com/llvm/llvm-project/pull/169742