[clang-tools-extra] [clangd] Add dynamic plugins support (PR #226995)

[via cfe-commits]

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

I have now reviewed this PR to the best of my ability (again, not that confident in my understanding of the general python test framework and cmake), but from my current understanding, LGTM. Not sure if you want to also have some comments from the other reviewers (if you ever get any), but otherwise feel free to merge.

https://github.com/llvm/llvm-project/pull/226995