[clang] [clang-tools-extra] [clangd] extend and rearrange doxygen hover documentation (PR #152918)

[via cfe-commits]

tcottin wrote:

@emaxx-google I think the error is fixed now, but I saw a -Wswitch warning I missed for the new `IncludeDirective` enumerator.
I pushed another change to fix this.
This disabled the auto merge. Could you look at it and approve again?

https://github.com/llvm/llvm-project/pull/152918