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

[Chuanqi Xu via cfe-commits]

ChuanqiXu9 wrote:

> I think clangd should reparse opened files, when dependent file changes (independent of is this include happens in preamble section or not). In this case clangd doesn't do this if include is not in the preamble section, so this looks like another problem.
> 
> This patch introduces ability to avoid preamble build and I think this works as expected. But yes, we found some problem cases but these problems have different origin. Anyway, this is just an option, which can be disabled/enabled.

If you think this is a missing feature, and the current patch introduces some problems but acceptable as modules support are experimental and we will add the feature back in the feature. Let's add them in document. And I think we can land this.

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