test(@angular/build): add e2e for tslib resolution in Vitest

Adds an end-to-end test to verify that tslib is correctly resolved
when using custom decorators within Vitest unit tests. This ensures
compatibility with Angular decorators and the Vitest runner's module
resolution configuration.

(cherry picked from commit f4a7cd9)

Author: clydin

tests/legacy-cli/e2e/tests/vitest/tslib-resolution.ts

@@ -0,0 +1,72 @@
+import { writeFile } from '../../utils/fs';
+import { installPackage } from '../../utils/packages';
+import { exec, ng } from '../../utils/process';
+import { applyVitestBuilder } from '../../utils/vitest';
+import assert from 'node:assert';
+
+export default async function () {
+  await applyVitestBuilder();
+  await installPackage('playwright@1');
+  await installPackage('@vitest/browser-playwright@4');
+  await exec('npx', 'playwright', 'install', 'chromium', '--only-shell');
+
+  // Add a custom decorator to trigger tslib usage
+  await writeFile(
+    'src/app/custom-decorator.ts',
+    `
+    export function MyDecorator() {
+      return function (target: any, propertyKey: string, descriptor: PropertyDescriptor) {
+        // do nothing
+      };
+    }
+    `,
+  );
+
+  // Add a service that uses the decorator
+  await writeFile(
+    'src/app/test.service.ts',
+    `
+    import { Injectable } from '@angular/core';
+    import { MyDecorator } from './custom-decorator';
+
+    @Injectable({
+      providedIn: 'root'
+    })
+    export class TestService {
+      @MyDecorator()
+      myMethod() {
+        return true;
+      }
+    }
+    `,
+  );
+
+  // Add a test for the service
+  await writeFile(
+    'src/app/test.service.spec.ts',
+    `
+    import { TestBed } from '@angular/core/testing';
+    import { TestService } from './test.service';
+
+    describe('TestService', () => {
+      let service: TestService;
+
+      beforeEach(() => {
+        TestBed.configureTestingModule({});
+        service = TestBed.inject(TestService);
+      });
+
+      it('should be created', () => {
+        expect(service).toBeTruthy();
+      });
+
+      it('myMethod should return true', () => {
+        expect(service.myMethod()).toBe(true);
+      });
+    });
+    `,
+  );
+
+  const { stdout } = await ng('test', '--no-watch', '--browsers', 'chromiumHeadless');
+  assert.match(stdout, /2 passed/, 'Expected 2 tests to pass.');
+}