[clangd] Add missing GoToStmt in FindTarget.

Summary: so that go-to-def on label can work.

Reviewers: sammccall

Subscribers: ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D77715