[clang-tools-extra] [clangd] Support outgoing calls in call hierarchy (PR #77556)

[Christian Kandeler via cfe-commits]

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

Appears to work fine.
Regarding the slight memory increase: If anyone feels strongly about it, they had plenty of time to chime in.

https://github.com/llvm/llvm-project/pull/77556