tag subclass tests with WeakSet and WeakMap (#2421)

test/language/statements/class/subclass/builtin-objects/WeakMap/regular-subclassing.js

@@ -14,6 +14,7 @@ info: |
   the WeakMap constructor to create and initialize the subclass instance with
   the internal state necessary to support the WeakMap.prototype built-in
   methods.
+features: [WeakMap]
 ---*/
 
 class WM extends WeakMap {}

test/language/statements/class/subclass/builtin-objects/WeakMap/super-must-be-called.js

@@ -14,6 +14,7 @@ info: |
   the WeakMap constructor to create and initialize the subclass instance with
   the internal state necessary to support the WeakMap.prototype built-in
   methods.
+features: [WeakMap]
 ---*/
 
 class M1 extends WeakMap {

test/language/statements/class/subclass/builtin-objects/WeakSet/regular-subclassing.js

@@ -14,6 +14,7 @@ info: |
   the WeakSet constructor to create and initialize the subclass instance with
   the internal state necessary to support the WeakSet.prototype built-in
   methods.
+features: [WeakSet]
 ---*/
 
 class WS extends WeakSet {}

test/language/statements/class/subclass/builtin-objects/WeakSet/super-must-be-called.js

@@ -14,6 +14,7 @@ info: |
   the WeakSet constructor to create and initialize the subclass instance with
   the internal state necessary to support the WeakSet.prototype built-in
   methods.
+features: [WeakSet]
 ---*/
 
 class WS1 extends WeakSet {