[clang-tools-extra] [clangd] Extend FeatureModule hooks (PR #221054)

[via cfe-commits]

https://github.com/timon-ul approved this pull request.

LGTM, the only thing I am still a bit unsure about is where to put the "justification" for these new functions. My first intuition would be to put it when these functions are used, e.g. when using `afterExecute` a comment that it has to wait for the preprocessor to be disconnected, which will be after the execute. So probably a thing to keep in mind for the follow up PR (when you move clang-tidy). Feel free to merge, unless you think this "justification" should still somehow be part of this PR (I am going on vacation so I am not gonna merge it anytime soon and didn't want to merge if you want to adjust this).

https://github.com/llvm/llvm-project/pull/221054