Improve property key query for Proxy objects (#3797)

Property key query for Proxy objects always returned all keys
even if no symbols were requested symbols were present in the
resulting array.

JerryScript-DCO-1.0-Signed-off-by: Peter Gal pgal.usz@partner.samsung.com

tests/jerry/es2015/regression-test-issue-3787.js

@@ -0,0 +1,22 @@
+// 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 symbol = Symbol("s");
+var obj = {demo: "3"};
+obj[symbol] = 3;
+
+var proxy = new Proxy(obj, []);
+var str = JSON.stringify(proxy);
+
+assert(str === '{"demo":"3"}');