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

[via cfe-commits]

timon-ul wrote:

> restricting the matches to constructor calls that occur in a `new` expression for now

Yeah makes sense.

> handle chained forwarding functions

I was thinking about this too, will for sure work on this as a followup task, seems a bit complicated again though, I think I now have to track where the parameter pack is going?

> we'll want some caching

I can't believe I forgot about the cache again....

> keeping around a `SmallSet<FunctionDecl*> SeenForwardingFuncInstances`

Is this right? Shouldn't it be a map mapping the declaration to the constructors? Because if I run across for example `make_unique<Foo>` a 2nd time I indeed do not need to traverse its body again, but I still need to record the current location as a reference to the constructor of `Foo`, right? 

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