Remove trailing newline from fenced code blocks

In some cases, `<pre><code>...\n</pre></code>` led to a trailing newline
in the code block as rendered by Tiptap.

Remove the trailing newline from HTML as serialized by markdown-it in
order to avoid this.

The other way round, while saving the file back, serializing to markdown
removes trailing newlines from code blocks anyway, so we don't have to
care about them.

Fixes: #2344

Signed-off-by: Jonas <jonas@freesources.org>

Author: mejo-

src/markdownit/index.js

@@ -16,4 +16,10 @@ const markdownit = MarkdownIt('commonmark', { html: false, breaks: false })
 	.use(keepSyntax)
 	.use(markdownitMentions)
 
+// Remove trailing newline from fenced code blocks (Github issue text#2344)
+const defaultFenceRule = markdownit.renderer.rules.fence
+markdownit.renderer.rules.fence = (...args) => {
+	return defaultFenceRule(...args).replace(/\n<\/code><\/pre>/, '</code></pre>')
+}
+
 export default markdownit