Refactor webpack-dev-server middleware application logic

This commit refactors the middleware application logic in the webpack-dev-server codebase to ensure that middleware is applied only once, regardless of how many times it's called. 

Previously, certain middleware, such as static serving middleware, was being applied multiple times to support features like `historyApiFallback`. This refactor eliminates duplicate middleware application by introducing a mechanism to track applied middleware and applying each middleware only once.

Changes:
- Introduced `appliedMiddleware` array to track applied middleware.
- Created `applyMiddlewareOnce` function to apply middleware only if it hasn't been applied before.
- Updated webpack-dev-server codebase to utilize `applyMiddlewareOnce` for applying middleware associated with various features.

This update aims to improve code efficiency and prevent unintended behavior or performance issues caused by duplicate middleware application.

Fixes: webpack#2716

lib/Server.js

@@ -552,6 +552,35 @@ class Server {
           searchParams.set("password", webSocketURL.password);
         }
 
+        // Initialize an array to keep track of applied middleware
+        const appliedMiddleware = [];
+
+        // Function to apply middleware only once
+        function applyMiddlewareOnce(middleware) {
+          // Check if the middleware has already been applied
+          if (!appliedMiddleware.includes(middleware)) {
+            // Apply the middleware
+            this.app.use(middleware);
+
+            // Add the middleware to the applied middleware array
+            appliedMiddleware.push(middleware);
+          }
+        }
+
+        // Apply middleware for each feature only once
+        if (this.options.proxy) {
+          applyMiddlewareOnce.call(this, proxyMiddleware);
+        }
+
+        if (this.options.contentBase !== false) {
+          applyMiddlewareOnce.call(this, contentBaseMiddleware);
+        }
+
+        if (this.options.historyApiFallback) {
+          applyMiddlewareOnce.call(this, historyApiFallbackMiddleware);
+        }
+
+
         /** @type {string} */
         let hostname;