Implement Object.prototype.__proto__ accessor property (#3546)

We are using the already existing Object.getPrototypeOf and
Object.setProtoypeOf methods

JerryScript-DCO-1.0-Signed-off-by: Adam Szilagyi aszilagy@inf.u-szeged.hu

tests/jerry/es2015/object-prototype-proto.js

@@ -0,0 +1,58 @@
+// Copyright JS Foundation and other contributors, http://js.foundation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+try {
+  eval('var o = { __proto__ : 5, __proto__ : 5 }');
+  assert(false);
+} catch (e) {
+  assert(e instanceof SyntaxError);
+}
+
+var f = function(){};
+assert((new f()).__proto__ === f.prototype);
+
+var o = {};
+o.__proto__ = Array.prototype;
+assert(o instanceof Array);
+
+var obj = Object.create(null) 
+p = {};
+obj.__proto__ = p;
+assert(Object.getPrototypeOf(obj) !== p);
+
+var Circle = function () {};
+var shape = {};
+var circle = new Circle();
+
+shape.__proto__ = circle;
+
+assert(Object.getPrototypeOf(shape) === circle);
+assert(shape.__proto__ === circle);
+
+assert(Object.prototype.hasOwnProperty('__proto__') === true);
+
+var desc = Object.getOwnPropertyDescriptor(Object.prototype,"__proto__");
+assert((desc && "get" in desc && "set" in desc && desc.configurable && !desc.enumerable) === true);
+
+assert((Object.getOwnPropertyNames(Object.prototype).indexOf('__proto__') > -1) === true);
+
+try {
+  shape.__proto__ = shape;
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+var o2 =  { ["__proto__"] : null };
+assert(o2.__proto__ === null);