Upgrade mdx to use last version of odoc-parser

[gpetiot]

Follow-up on #430

• [x] update script updated
• [x] vendored parser updated
• [x] mdx compiles
• [x] use the new syntax for block output

Re-using code from https://github.com/realworldocaml/mdx/compare/main...jonludlam:mdx:vendor-odoc-parser-richmdx

[jonludlam]

I don't think we should delete the license file from the vendored parser

[Leonidas-from-XIV]

It's weird that it doesn't fail, given there is a line to copy LICENSE.md and the script is set -e.

[gpetiot]

The update script is now copying the license file from odoc (longer than the previous one)