Render embedded code preview by permlink in markdown (#30234)

The permlink in markdown will be rendered as a code preview block, like GitHub

Co-authored-by: silverwind <me@silverwind.io>

web_src/css/index.css

@@ -41,6 +41,7 @@
 
 @import "./markup/content.css";
 @import "./markup/codecopy.css";
+@import "./markup/codepreview.css";
 @import "./markup/asciicast.css";
 
 @import "./chroma/base.css";