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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@HighCommander4 No problem, I'm always delighted to receive responses! However it might take me some time to pick up my thoughts, as the patch has been a while. Anyway, I will try to revive this patch in the next few days and let's see if we can make it into clangd 19.

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