[clang-tools-extra] [wip][clangd] Introduce --skip-preamble-build command line option (PR #189284)

[Chuanqi Xu via cfe-commits]

https://github.com/ChuanqiXu9 commented:

But in the current impl, for module units containing headers, how can clangd detect the change in the included header for the module units?

https://github.com/llvm/llvm-project/pull/189284