WebServer: Append trailing slash for directory links

This adds trailing slashes to all links to directories (when listing the
directory contents). This avoids the redirect that would otherwise
happen when browsing to those directories.

Author: MaxWipfli

Userland/Services/WebServer/Client.cpp

@@ -237,6 +237,10 @@ void Client::handle_directory_listing(String const& requested_path, String const
         builder.appendff("<td><div class=\"{}\"></div></td>", is_directory ? "folder" : "file");
         builder.append("<td><a href=\"");
         builder.append(URL::percent_encode(name));
+        // NOTE: For directories, we append a slash so we don't always hit the redirect case,
+        //       which adds a slash anyways.
+        if (is_directory)
+            builder.append('/');
         builder.append("\">");
         builder.append(escape_html_entities(name));
         builder.append("</a></td><td>&nbsp;</td>");