[clang-tools-extra] Refactor clang doc comment structure (PR #142273)

[Samarth Narang via cfe-commits]

snarang181 wrote:

> Oh, lets updated the PR description with a more complete description of the change. It can also be marked as `Fixes #NNN` since this basically implements everything outlined in the issues, unless I'm forgetting something.

Done.

https://github.com/llvm/llvm-project/pull/142273