[clang-tools-extra] [clangd] Change completion-style default to detailed (PR #195963)

[Nathan Ridge via cfe-commits]

https://github.com/HighCommander4 commented:

Could you add a release note to https://github.com/llvm/llvm-project/blob/main/clang-tools-extra/docs/ReleaseNotes.rst#improvements-to-clangd please? This helps users who liked the previous behaviour discover how to restore it.

Otherwise LGTM. We do have some test coverage of the `detailed` behaviour, even if it's implicit (e.g. [here](https://searchfox.org/llvm/rev/0c274303e358a136fbdd3e6276e9097b917eae4b/clang-tools-extra/clangd/unittests/CodeCompleteTests.cpp#2854-2863)), I'm happy with that.

https://github.com/llvm/llvm-project/pull/195963