[clang] [Documentation] Replace recommonmark by myst-parser (PR #65664)

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cor3ntin wrote:

Agreed. I have found that the full set of needed pip modules is
`sphinx myst-parser sphinx-markdown-tables sphinx-automodapi furo` - I think most of theses are only used by LLDB but might as well document them as requirements for everything.

https://github.com/llvm/llvm-project/pull/65664