Fix: Provide default angular export for plugins (#75424)

fix(plugins): provide default export of angular for old system.register plugins

public/app/angular/AngularApp.ts

@@ -25,7 +25,10 @@ import { registerComponents } from './registerComponents';
 
 // Angular plugin dependencies map
 const importMap = {
-  angular: angular,
+  angular: {
+    ...angular,
+    default: angular,
+  },
   'app/core/core_module': {
     default: coreModule,
     __useDefault: true,