fix: Assign proper namespaces to foreignObject children

[lishid]

📑 Summary

This fixes a bug where if the mermaid diagram is rendered directly (without being taken out as innerHTML and going through the HTML parser again after it was first rendered), journey diagrams will not properly show task text, due to these foreignObjects being created in the svg namespace. This patch adds the xhtml namespace for the div elements so that they are created in the proper namespace.

Illustration of the problem:

📏 Design Decisions

Inspired by the usage of xhtml:div here:

mermaid/src/dagre-wrapper/createLabel.js

Line 65 in e6e94ad

const div = fo.append('xhtml:div');

📋 Tasks

Make sure you

• 📖 have read the contribution guidelines
• 💻 have added unit/e2e tests (if appropriate)
• 🔖 targeted develop branch