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

[kadir çetinkaya via cfe-commits]

https://github.com/kadircet approved this pull request.

thanks, mostly LG! i think not leaving the default parameter values are important here to make sure we don't forget to pass the top-level config in any of the relevant places (both now, but also in the future). i know it probably comes with a bunch of changes to tests though :/ (i wish clangd was better at updating signatures in such cases!)

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