fix(@schematics/angular): retain trailing comma when adding providers to app config

This fixes an issue which caused the new provider to be added in the position of the traling comma. With this change the trailing comma is retained.

Closes angular#26911

Author: alan-agius4

packages/schematics/angular/utility/standalone/rules.ts

@@ -231,12 +231,10 @@ function addProvidersExpressionToAppConfig(
   // If there's a `providers` property, we can add the provider
   // to it, otherwise we need to declare it ourselves.
   if (providersLiteral) {
-    const hasTrailingComma = providersLiteral.elements.hasTrailingComma;
-
     applyChangesToFile(tree, filePath, [
       insertAfterLastOccurrence(
         providersLiteral.elements,
-        (hasTrailingComma || providersLiteral.elements.length === 0 ? '' : ', ') + expression,
+        (providersLiteral.elements.length === 0 ? '' : ', ') + expression,
         filePath,
         providersLiteral.getStart() + 1,
       ),

packages/schematics/angular/utility/standalone/rules_spec.ts

@@ -445,5 +445,36 @@ describe('standalone utilities', () => {
       assertContains(content, `import { provideModule } from '@my/module';`);
       assertContains(content, `providers: [provideModule([])]`);
     });
+
+    it('should add a root provider to a standalone app when has trailing comma', async () => {
+      await setupProject(true);
+
+      const configPath = 'app/app.config.ts';
+      host.overwrite(
+        getPathWithinProject(configPath),
+        `
+        import { ApplicationConfig } from '@angular/core';
+        import { provideRouter } from '@angular/router';
+
+        export const appConfig: ApplicationConfig = {
+          providers: [
+            provideRouter([]),
+          ]
+        };
+      `,
+      );
+
+      await testRule(
+        addRootProvider(
+          projectName,
+          ({ code, external }) => code`${external('provideModule', '@my/module')}([])`,
+        ),
+        host,
+      );
+
+      const content = readFile('app/app.config.ts');
+      assertContains(content, `import { provideModule } from '@my/module';`);
+      assertContains(content, `providers: [provideRouter([]),provideModule([]),]`);
+    });
   });
 });