Redmine

Redmine can now render Mermaid code blocks as diagrams (#44425), but the wiki syntax help pages do not mention it yet, so users cannot learn about it from the help.

The attached patch adds a description of Mermaid diagrams to both help pages:

• Wiki Syntax Quick Reference (/help/wiki_syntax): A new "Mermaid diagrams" row shows a short example and its rendered result.
• Wiki formatting (/help/wiki_syntax/detailed): A new "Mermaid diagrams" section explains the following points: * Code blocks in the "mermaid" language are rendered as diagrams by Mermaid.js. The section links to the Mermaid syntax reference. * Mermaid.js is not bundled with Redmine. Diagrams are rendered only if the administrator has installed it. Otherwise, the code is displayed as a plain code block. * A rendered diagram can be downloaded as a PNG image.

The help pages do not load JavaScript, so the example diagrams are included as PNG images. These images were saved with the download link of rendered diagrams, so they look the same as what users see, and they can be regenerated in the same way.

The changes cover both the Textile and the CommonMark Markdown help pages. The English and Japanese pages are updated, and the pages for other languages include the English text until they are translated. The labels in the example images are in English and are shared by all languages.