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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

Thanks for the prompt and insightful feedback; I really appreciate it! There are a lot of comments, so it takes some time to digest them. I'll make an effort to address them in the coming days.

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