Use eager import to include client modules (#35979)

Eager import does almost the same thing as `require()` but it instead also supports loading an ES module.

## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

packages/next/build/webpack/loaders/next-flight-server-loader.ts

@@ -238,7 +238,12 @@ export default async function transformSource(
       __webpack_require__,
       _: () => {
         ${imports
-          .map((importSource) => `require('${importSource}');`)
+          .map(
+            (importSource) =>
+              `import(/* webpackMode: "eager" */ ${JSON.stringify(
+                importSource
+              )});`
+          )
           .join('\n')}
       },
       server: ${isServerExt ? 'true' : 'false'}