fix(@angular-devkit/build-angular): avoid build performance hit when using custom loader

loaders in esbuild aren't really custom code. You can only choose from the loaders that esbuild provides. So I doubt they require this `externalPackagesPlugin` which comes at a pretty steep cost of 1 second per 1500 imports your project has on every build and watch rebuild.

fixes angular#27116

Author: sod

packages/angular_devkit/build_angular/src/tools/esbuild/application-code-bundle.ts

@@ -65,9 +65,8 @@ export function createBrowserCodeBundleOptions(
   }
 
   if (options.externalPackages) {
-    // Package files affected by a customized loader should not be implicitly marked as external
+    // Package files affected by a customized plugin should not be implicitly marked as external
     if (
-      options.loaderExtensions ||
       options.plugins ||
       typeof options.externalPackages === 'object'
     ) {