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

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