[clang-tools-extra] [clangd] Support go-to-definition on type hints. The core part (PR #86629)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 requested changes to this pull request.

(@zyn0217 I'm going to mark this as "Request changes" to reflect my understanding from the previous comment that the next step here is you splitting up the patch. If I've misunderstood and you'd like me to have a look at the current version, let me know!)

https://github.com/llvm/llvm-project/pull/86629