perf: Rewriting convert_deflists for performance.

markdown/testdata/deflists/reference/pandoc/04-markdown-in-def.html

@@ -0,0 +1,9 @@
+<dl>
+<dt>Markdown Syntax</dt>
+<dd>
+<strong>Markdown</strong> supports multiple text formatting: -
+<em>Italic</em> and <strong>Bold</strong> - <a
+href="https://www.markdownlang.com">Link</a> - <code>Inline code</code>
+- &gt; Block quote - Lists and other elements
+</dd>
+</dl>