Implement the Set builtin object (#2841)

Also implement the missing iterator initializer part from the Map builtin object constructor.

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

tests/jerry/es2015/map.js

@@ -117,3 +117,9 @@ assert(mapNameDesc.enumerable === false);
 assert(mapNameDesc.configurable === true);
 
 assert(Map.prototype.name === undefined);
+
+m = new Map([{0: "foo", 1: 3}, {0 : "bar", 1 : 2}]);
+
+assert (m.size === 2);
+assert (m.get("foo") === 3);
+assert (m.get("bar") === 2);