feat(@schematics/angular): add export to renderModule in server main file

This will be used by universal and app-shell to render the server module

Author: alan-agius4

packages/schematics/angular/universal/files/src/__main@stripTsExtension__.ts.template

@@ -7,3 +7,4 @@ if (environment.production) {
 }
 
 export { <%= rootModuleClassName %> } from './app/<%= stripTsExtension(rootModuleFileName) %>';
+export { renderModule } from '@angular/platform-server';