[dart:js_interop] Non-empty @JSExport on class should not be a fatal error

Fixes #61291

Change-Id: I5a5c058cfe46880704912145b2ec98b19127282d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/445101
Commit-Queue: Erik Ernst <[email protected]>
Auto-Submit: Srujan Gaddam <[email protected]>
Reviewed-by: Erik Ernst <[email protected]>

Author: srujzs

pkg/_js_interop_checks/lib/src/transformations/export_checker.dart

@@ -125,7 +125,6 @@ class ExportChecker {
         cls.name.length,
         cls.location?.file,
       );
-      exportStatus[cls.reference] = ExportStatus.exportError;
     }
 
     _collectOverrides(cls);

tests/lib/js/export/functional_test.dart

@@ -11,7 +11,9 @@ import 'package:expect/legacy/minitest.dart'; // ignore: deprecated_member_use_f
 import 'package:js/js_util.dart';
 
 // Test exporting all vs. only some members.
-@JSExport()
+// Also test using a non-empty `@JSExport` annotation on a class, which should
+// be a warning but should not prevent code generation.
+@JSExport('A')
 class ExportAll {
   ExportAll.constructor();
   factory ExportAll.factory() => ExportAll.constructor();