Remove the click-to-copy data attribute

[chriszarate]

• Remove the click-to-copy data attribute from the GitHub Markdown block example.
  • This data attribute contained a copy of the code in the following code fence, which GitHub uses to implement click-to-copy. GitHub properly escapes this attribute using HTML entities, but our DOM parser (used to fix Markdown links) renders them unescaped. When this attribute contains HTML markup, it ends up being rendered on the page. We don't use this attribute, so we can just remove it.

• Remove the XML declaration after processing. The XML attribute was being rendered in the block editor.
• Correctly map example code in VS Code settings so that example code can be debugged.

[github-actions]

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