cherry-pick(#27630): fix: merge{Tests,Expects} via ESM imports (#27641)

This PR cherry-picks the following commits:

- fd2fbe9d2f

Co-authored-by: github-actions <41898282+github-actions[bot]@users.noreply.github.com>

packages/playwright/test.mjs

@@ -28,4 +28,6 @@ export const _android = playwright._android;
 export const test = playwright.test;
 export const expect = playwright.expect;
 export const defineConfig = playwright.defineConfig;
+export const mergeTests = playwright.mergeTests;
+export const mergeExpects = playwright.mergeExpects;
 export default playwright.test;

tests/playwright-test/esm.spec.ts

@@ -632,3 +632,43 @@ test('should be able to use use execSync with a Node.js file inside a spec', asy
     'fork: hello from hellofork.js',
   ]);
 });
+
+test('should be able to use mergeTests/mergeExpect', async ({ runInlineTest }) => {
+  const result = await runInlineTest({
+    'a.test.mjs': `
+      import { test as base, expect as baseExpect, mergeTests, mergeExpects } from '@playwright/test';
+      const test = mergeTests(
+        base.extend({
+          myFixture1: '1',
+        }),
+        base.extend({
+          myFixture2: '2',
+        }),
+      );
+
+      const expect = mergeExpects(
+        baseExpect.extend({
+          async toBeFoo1(page, x) {
+            return { pass: true, message: () => '' };
+          }
+        }),
+        baseExpect.extend({
+          async toBeFoo2(page, x) {
+            return { pass: true, message: () => '' };
+          }
+        }),
+      );
+
+      test('merged', async ({ myFixture1, myFixture2 }) => {
+        console.log('%%myFixture1: ' + myFixture1);
+        console.log('%%myFixture2: ' + myFixture2);
+        await expect(1).toBeFoo1();
+        await expect(1).toBeFoo2();
+      });
+    `,
+  });
+  expect(result.exitCode).toBe(0);
+  expect(result.passed).toBe(1);
+  expect(result.outputLines).toContain('myFixture1: 1');
+  expect(result.outputLines).toContain('myFixture2: 2');
+});