refactor: use public API (#3320)

Author: snitin315

lib/Server.js

@@ -1037,16 +1037,10 @@ class Server {
   }
 
   serveMagicHtml(req, res, next) {
-    const getFilenameFromUrl =
-      require('webpack-dev-middleware/dist/utils/getFilenameFromUrl').default;
-
     const _path = req.path;
 
     try {
-      const filename = getFilenameFromUrl(
-        this.middleware.context,
-        `${_path}.js`
-      );
+      const filename = this.middleware.getFilenameFromUrl(`${_path}.js`);
       const isFile = this.middleware.context.outputFileSystem
         .statSync(filename)
         .isFile();