Splits markdown text into ```mermaid fenced-code blocks and the (markdown) text around them.
Only mermaid fences are separated out. Every other construct - including non-mermaid code fences -
stays within the surrounding markdown segments so it keeps rendering as before.
Splits markdown text into ```mermaid fenced-code blocks and the (markdown) text around them. Only mermaid fences are separated out. Every other construct - including non-mermaid code fences - stays within the surrounding markdown segments so it keeps rendering as before.