[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 (#156365)
Fixes some followup issues from clangd/clangd#529.
`\note` and `\warning`:
In the hover card, they are now displayed with heading and enclosing
rulers.
`\retval` commands:
Each `\retval` command is now a bullet point under the return section of
the hover card.
Added a Markdown preprocessing step before parsing the documentation
with the doxygen parser.
This mainly replaces markdown code blocks with `@code...@endcode`
commands.
llvm-project
8a505a11 - [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 (#156365)
