Add new error message for awaiting the client export (#29853)

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## Summary

`Cannot access .then on server` is not an ideal message when you try to
await or do promise chain to the properties of client reference. The
below example will let `.then` get accessed by native code while
handling the promise chain but the access is not clearly visible in user
code.

```
import('./client-module').then((mod) => mod.Component)
```

This PR chnage the error message of module reference proxy '.then'
property to show more kinds of usage, then it can be pretty clearly for
helping users to avoid the bad usage

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## How did you test this change?

Unit test

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packages/react-server-dom-turbopack/src/ReactFlightTurbopackReferences.js

@@ -133,6 +133,11 @@ const deepProxyHandlers = {
             `Instead, you can export a Client Component wrapper ` +
             `that itself renders a Client Context Provider.`,
         );
+      case 'then':
+        throw new Error(
+          `Cannot await or return from a thenable. ` +
+            `You cannot await a client module from a server component.`,
+        );
     }
     // eslint-disable-next-line react-internal/safe-string-coercion
     const expression = String(target.name) + '.' + String(name);

packages/react-server-dom-webpack/src/ReactFlightWebpackReferences.js

@@ -141,6 +141,11 @@ const deepProxyHandlers = {
             `Instead, you can export a Client Component wrapper ` +
             `that itself renders a Client Context Provider.`,
         );
+      case 'then':
+        throw new Error(
+          `Cannot await or return from a thenable. ` +
+            `You cannot await a client module from a server component.`,
+        );
     }
     // eslint-disable-next-line react-internal/safe-string-coercion
     const expression = String(target.name) + '.' + String(name);

packages/react-server-dom-webpack/src/__tests__/ReactFlightDOM-test.js

@@ -623,6 +623,20 @@ describe('ReactFlightDOM', () => {
     );
   });
 
+  it('throws when await a client module prop of client exports', async () => {
+    const ClientModule = clientExports({
+      Component: {deep: 'thing'},
+    });
+    async function awaitExport() {
+      const mod = await ClientModule;
+      return await Promise.resolve(mod.Component);
+    }
+    await expect(awaitExport()).rejects.toThrowError(
+      `Cannot await or return from a thenable. ` +
+        `You cannot await a client module from a server component.`,
+    );
+  });
+
   it('throws when accessing a symbol prop from client exports', () => {
     const symbol = Symbol('test');
     const ClientModule = clientExports({