fix(@angular/build): automatically resolve .mjs files when using Vite

Previously, ESM file resolution without extensions failed when using Vite, causing issues in module loading. This commit addresses the problem by automatically resolving `.mjs` files, aligning the behavior with the application builder and ensuring consistent module resolution across different build tools.

Closes #27841

Author: alan-agius4

packages/angular/build/src/builders/dev-server/vite-server.ts

@@ -677,6 +677,7 @@ function getDepOptimizationConfig({
       supported: getFeatureSupport(target, zoneless),
       plugins,
       loader,
+      resolveExtensions: ['.mjs', '.js'],
     },
   };
 }