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

[Andrei Lebedev via cfe-commits]

andreil99 wrote:

I can update the publishing bots. For the bots running on https://lab.llvm.org/buildbot/#/workers/92 we would need @gribozavr or somebody with access to gribozavr3 worker.

@cor3ntin, is there any dependency on a particular version of myst-parser?

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