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

[Andrei Lebedev via cfe-commits]

andreil99 wrote:

@cor3ntin No, I did not update all the sphinx bots, only specific ones, as I mentioned above in https://github.com/llvm/llvm-project/pull/65664#issuecomment-1714983618
> 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.

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