Expose the Server instance through the pluggable Builder API

Builder implementations (e.g. Vite) may have hot module replacement
implementations based on Websockets. The websocket has to be mounted
on the Server instance - which is why the builder needs access to
it from the API.

lib/core-common/src/types.ts

@@ -169,6 +169,7 @@ export interface Builder<Config, Stats> {
     options: Options;
     startTime: ReturnType<typeof process.hrtime>;
     router: Router;
+    server: Server;
   }) => Promise<void | {
     stats: Stats;
     totalTime: ReturnType<typeof process.hrtime>;

lib/core-server/src/dev-server.ts

@@ -59,12 +59,14 @@ export async function storybookDevServer(options: Options) {
         startTime,
         options,
         router,
+        server,
       });
 
   const manager = managerBuilder.start({
     startTime,
     options,
     router,
+    server,
   });
 
   const [previewResult, managerResult] = await Promise.all([