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

[Nathan Ridge via cfe-commits]

HighCommander4 wrote:

Since Phabricator has been [taken down](https://discourse.llvm.org/t/llvm-phabricator-turndown/76137), I'm resubmitting the patch implementing outgoing calls in call hierarchy that was previously posted at https://reviews.llvm.org/D93829.

Previous discussion can still be seen at the Phabricator link which now links to a static snapshot of the review.

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