Add Class.isEnum to Kernel and use it to resynthesize enums in Analyzer.

pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart

Index: pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
diff --git a/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart b/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
index b649a3fddc3e3ca9f75ec7cbdef97ccd28b70633..1ab61cf829025e186956f70fbeb9baa8b30ee5e5 100644
--- a/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
+++ b/pkg/analyzer/test/src/summary/resynthesize_kernel_test.dart
@@ -298,16 +298,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
   }
 
   @failingTest
-  test_constExpr_pushReference_enum_field() async {
-    await super.test_constExpr_pushReference_enum_field();
-  }
-
-  @failingTest
-  test_constExpr_pushReference_enum_method() async {
-    await super.test_constExpr_pushReference_enum_method();
-  }
-
-  @failingTest
   test_constructor_initializers_assertInvocation() async {
     await super.test_constructor_initializers_assertInvocation();
   }
@@ -414,16 +404,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
   }
 
   @failingTest
-  test_enum_values() async {
-    await super.test_enum_values();
-  }
-
-  @failingTest
-  test_enums() async {
-    await super.test_enums();
-  }
-
-  @failingTest
   test_error_extendsEnum() async {
     await super.test_error_extendsEnum();
   }
@@ -946,11 +926,6 @@ class ResynthesizeKernelStrongTest extends ResynthesizeTest {
   }
 
   @failingTest
-  test_type_reference_to_enum() async {
-    await super.test_type_reference_to_enum();
-  }
-
-  @failingTest
   test_type_reference_to_import() async {
     await super.test_type_reference_to_import();
   }