[clang-tools-extra] [clangd] Doxygen Parsing: Add proper handling of \note, \warning and \retval command + change render kind of command arguments + add preprocessing for markdown code blocks/spans (PR #156365)

[Hsin-chieh Liu via cfe-commits]

Stehsaer wrote:

> @Stehsaer I implemented the separation. Please give it a try.
> 
> For simplicity, I use the first paragraph in case there is no brief command and the first paragraph is not a block command. This is not exactly the same as with doxygen `JAVADOC_AUTOBRIEF==YES` but I think its good this way.

Just tried it out and tested over my codebases, it's working greater than expected! Although it doesn't perfectly align with the purpose of the original `@details`, but it is working even better than the original, at least in all my testcases. All briefs and details inside the comments are separated nicely and expectedly. 

https://github.com/llvm/llvm-project/pull/156365