[clang-tools-extra] [clangd] Re-land "support outgoing calls in call hierarchy" (PR #117673)

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

> relanded with benchmark fix in [61fe67a](https://github.com/llvm/llvm-project/commit/61fe67a4017375fd675f75652e857e837f77fa51)
> 
> changed required -> optional in [c7ef0ac](https://github.com/llvm/llvm-project/commit/c7ef0ac9fd28cb55b8c7c91a890b365cc688f9a9)

Thanks!

https://github.com/llvm/llvm-project/pull/117673