Update ES6 Regexp accessors descriptors (#3726)

In ES6 accessors of built in object are by default configurable.
Also lastIndex property of RegExp object is created when only used.

JerryScript-DCO-1.0-Signed-off-by: Rafal Walczyna r.walczyna@samsung.com

tests/jerry/es2015/regexp-accessors-descriptors.js

@@ -0,0 +1,23 @@
+// 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 accessors = [ 'flags', 'global', 'ignoreCase', 'multiline', 'source', 'sticky', 'unicode' ]
+
+accessors.forEach(function(attr) {
+    var desc = Object.getOwnPropertyDescriptor(RegExp.prototype, attr);
+    assert(typeof desc.get === 'function')
+    assert(desc.set === undefined)
+    assert(desc.enumerable === false)
+    assert(desc.configurable === true)
+});

tests/jerry/es2015/regexp-lastindex.js

@@ -18,3 +18,5 @@ result = t.exec("abc   abc");
 assert(result[0] === "abc");
 assert(result.index === 0);
 assert(t.lastIndex === 3);
+
+assert(RegExp.prototype.lastIndex === undefined)