[clang-tools-extra] [clangd] Add config option to allow detection of unused system headers (PR #87208)

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

I think I'm fine with it as-is, but we probably need include-cleaner folks to approve it. (That means you probably have to wait a few more weeks for them, unfortunately.)

https://github.com/llvm/llvm-project/pull/87208