Myst-vs-code blocks plantuml rendering for code blocks

[arwedus]

Describe the bug

With the jebbs.plantuml extension and the VS Code internal Markdown preview,
the following code will produce a rendered inline plantUML diagram inside the markdown preview:

# My diagram document

This should render as an inline diagram in VS code markdown preview:

```{uml}
@startuml
A -> B
B -> A
@enduml
```

With myst markdown extension enabled (and myst.preview.enable enabled), the above code block is instead rendered as some text block hovering on the right side of the document preview.

With the setting myst.preview.enable set to false, plantUML code blocks like above are rendered as diagrams again.

To Reproduce

1. Install extension jebbs.plantuml
2. Configure the plantuml rendering mode to "server" ("local" rendering in Markdown preview won't work)
3. Create a new markdown file with the content given above
4. Open Markdown preview to the side

Expected behavior

myst-vs-code should probably forward all "sphinx directives code blocks" for which it doesn't have any special handling to the default markdown renderer. Especially for directives uml, plantuml. However, there are other directives like mermaid for which there might be a special rendering in VS Code.

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 20.04 Linux
• VS Code Version v1.75.0
• Myst markdown v0.11.0

[welcome]

Thanks for opening your first issue here! Engagement like this is essential for open source projects! 🤗

If you haven't done so already, check out EBP's Code of Conduct. Also, please try to follow the issue template as it helps other community members to contribute more effectively.

If your issue is a feature request, others may react to it, to raise its prominence (see Feature Voting).

Welcome to the EBP community! 🎉