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

[Younan Zhang via cfe-commits]

zyn0217 wrote:

@HighCommander4 Sorry for my delay. This is ready for the next round of review, and I'm prepared for a lot of feedback!

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