[clangd] Support go-to-definition on type hints. The protocol part (#85497)

This is in preparation for implementing go-to-definition support on type
inlay hints, switching the `label` field within the InlayHint protocol from a
string to an array of `InlayHintLabelPart`.

GitOrigin-RevId: c6a65e4b0c80245d766ae2f2f7305b5371d096f5
7 files changed