[tests] Primary constructors - Allow ; bodies on any membered declarations.

Updating some primary constructor tests in light of issue 4645 that allows `;` on any membered declarations.

Bug: https://github.com/dart-lang/language/issues/4645, https://github.com/dart-lang/sdk/issues/61687
Change-Id: I390ccd1eb1c84d55ee599d4d94ab199bb4920880
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/485585
Commit-Queue: Kallen Tu <kallentu@google.com>
Reviewed-by: Erik Ernst <eernst@google.com>

tests/language/primary_constructors/syntax/empty_body_error_test.dart

@@ -2,28 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// For mixins, an empty body, `{}`, cannot be replaced by `;`. Enums require a
-// non-empty declaration.
+// Enums that have an empty body (i.e. `;`) can be parsed, but will cause a
+// compile-time error when there's no enum constant declared.
 
 // SharedOptions=--enable-experiment=primary-constructors
 
-class C1;
-
-mixin M1;
-//    ^
-// [analyzer] unspecified
-// [cfe] unspecified
-
-mixin M2 implements C1;
-//    ^
-// [analyzer] unspecified
-// [cfe] unspecified
-
-mixin M3 on C1;
-//    ^
-// [analyzer] unspecified
-// [cfe] unspecified
-
 enum E1;
 //   ^
 // [analyzer] unspecified

tests/language/primary_constructors/syntax/empty_body_test.dart

@@ -2,28 +2,56 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// An empty class body, `{}`, can be replaced by `;`.
+// An empty declaration body, `{}`, can be replaced by `;`.
 
 // SharedOptions=--enable-experiment=primary-constructors
 
+// Classes
 class C1;
 
 class C2 with M1;
 
 class C3(var int x) extends C1;
 
-mixin class M1 implements C1;
-
-mixin class M2;
-
+// Extension types
 extension type E1(int x);
 
 extension type const E2(int x);
 
+// Mixin classes
+mixin class M1 implements C1;
+
+class M1With with M1;
+
+mixin class M2;
+
+class M2With with M2;
+
+// Mixins
+mixin M3;
+
+class M3With with M3;
+
+mixin M4 implements C1;
+
+class M4With with M4;
+
+mixin M5 on C1;
+
+class M5With extends C1 with M5;
+
+// Extension
+extension Ext1 on C1;
+
 void main() {
   print(C1());
   print(C2());
   print(C3(1));
   print(E1(1));
   print(E2(1));
+  print(M1With());
+  print(M2With());
+  print(M3With());
+  print(M4With());
+  print(M5With());
 }