ES6: Add support for Map.prototype.forEach and Set.prototype.forEach

src/macros.py

Index: src/macros.py
diff --git a/src/macros.py b/src/macros.py
index 0b69e6b80e436d477d8a94867d07071bd221101a..2a7dbddd587eed2a2b67d30235e5c9961ec01c33 100644
--- a/src/macros.py
+++ b/src/macros.py
@@ -272,3 +272,8 @@ const PROPERTY_ATTRIBUTES_NONE = 0;
 const PROPERTY_ATTRIBUTES_STRING = 8;
 const PROPERTY_ATTRIBUTES_SYMBOLIC = 16;
 const PROPERTY_ATTRIBUTES_PRIVATE_SYMBOL = 32;
+
+# Use for keys, values and entries iterators.
+const ITERATOR_KIND_KEYS = 1;
+const ITERATOR_KIND_VALUES = 2;
+const ITERATOR_KIND_ENTRIES = 3;