Implement WeakRef Object (#4546)

Related test262 test-cases has been removed from skip list.
Execpt two test-case since they need other feature to work (Finalization registry and async GC)

JerryScript-DCO-1.0-Signed-off-by: Bence Gabor Kis kisbg@inf.u-szeged.hu

tests/jerry/es.next/weakref.js

@@ -0,0 +1,69 @@
+// 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.
+
+var target_obj = {};
+var not_target_obj = {};
+var weak_ref = new WeakRef(target_obj);
+var weak_ref2 = new WeakRef(target_obj);
+
+assert (weak_ref.deref() === target_obj);
+assert (weak_ref.deref() === weak_ref2.deref());
+assert (weak_ref.deref() !== not_target_obj);
+
+assert (weak_ref2.deref() === target_obj);
+assert (weak_ref2.deref() !== not_target_obj);
+assert (weak_ref2.deref() === weak_ref2.deref());
+
+target_obj = undefined;
+gc();
+
+assert (weak_ref.deref() === undefined);
+assert (weak_ref2.deref() === undefined);
+
+var key_obj_1 = {};
+var key_obj_2 = {};
+var key_obj_3 = {};
+var target_obj_2 = {};
+var target_obj_3 = {};
+var weak_ref_3 = new WeakRef(key_obj_1);
+var weak_ref_4 = new WeakRef(target_obj_2);
+var weak_ref_5 = new WeakRef(target_obj_3);
+
+var weak_map = new WeakMap();
+weak_map.set(key_obj_1, weak_ref_3);
+weak_map.set(key_obj_2, weak_ref_4);
+weak_map.set(key_obj_3, weak_ref_5);
+
+assert(weak_map.has(key_obj_1));
+assert(weak_map.has(key_obj_2));
+assert(weak_map.has(key_obj_3));
+
+assert(weak_map.get(key_obj_1).deref() === key_obj_1);
+assert(weak_map.get(key_obj_2).deref() === target_obj_2);
+assert(weak_map.get(key_obj_3).deref() === target_obj_3);
+
+key_obj_1 = undefined;
+gc();
+assert(weak_map.get(key_obj_1) === undefined);
+assert(weak_ref_3.deref() === undefined);
+
+key_obj_2 = undefined;
+gc();
+assert(weak_map.get(key_obj_2) === undefined);
+assert(weak_ref_4.deref() === target_obj_2);
+
+target_obj_3 = undefined;
+gc();
+assert(weak_map.get(key_obj_3) !== undefined);
+assert(weak_ref_5.deref() === undefined);