Fix unrelated_type_equality_checks when comparing enums

lib/src/util/dart_type_utilities.dart

@@ -288,8 +288,16 @@ extension on TypeSystem {
       // Otherwise, they might be related.
       return false;
     } else {
+      var sameSupertypes = leftElement.supertype == rightElement.supertype;
+
+      // Unrelated Enums have the same supertype, but they are not the same element, so
+      // they are unrelated.
+      if (sameSupertypes && leftElement is EnumElement) {
+        return true;
+      }
+
       return (leftElement.supertype?.isDartCoreObject ?? false) ||
-          leftElement.supertype != rightElement.supertype;
+          !sameSupertypes;
     }
   }
 }

test_data/rules/unrelated_type_equality_checks.dart

@@ -167,7 +167,7 @@ void function23() {
 }
 
 void function30() {
-  ClassWMethod c =  ClassWMethod();
+  ClassWMethod c = ClassWMethod();
   if (c.determinant == 0.0) print('someFunction30'); // LINT
   if (c.determinant == double) print('someFunction30'); // LINT
   if (c.determinant == c.determinspider) print('someFunction30'); // OK
@@ -178,6 +178,24 @@ void function30() {
   if (c.determinant == callable2) print('someFunction30'); // OK
 }
 
+void function31() {
+  var x = EnumOpKind1.delete;
+  if (x == EnumOpKind1.delete) print('delete'); // OK
+  if (x == EnumOpKind1.update) print('update'); // OK
+  if (x == EnumOpKind2.delete) print('delete'); // LINT
+  if (x == 'delete') print('delete'); // LINT
+}
+
+void function32() {
+  var x = EnumImplements.a;
+  if (x == EnumImplements.a) print('a'); // OK
+  if (x == EnumImplements.b) print('b'); // OK
+  if (x == EnumMixin.b) print('b'); // LINT
+
+  var y = EnumMixin.a;
+  if (y == EnumImplements.a) print('a'); // LINT
+}
+
 class ClassBase {}
 
 class DerivedClass1 extends ClassBase {}
@@ -203,3 +221,11 @@ class ClassWCall {
 }
 
 class SubClassWCall extends ClassWCall {}
+
+enum EnumOpKind1 { insert, update, delete }
+
+enum EnumOpKind2 { upsert, delete }
+
+enum EnumImplements implements ClassBase { a, b, c }
+
+enum EnumMixin with Mixin { a, b, c }