Re-target for ES.Next (#3901)

A list of changes:
- 'es2015-subset' profile is deprecated, and an 'es.next' profile is added.
- The default profile is changed to 'es.next'
- Renamed the JERRY_ES2015 guard to JERRY_ESNEXT
- Renamed JERRY_ES2015_BUILTIN_* guards to JERRY_BUILTIN_*
- Moved es2015 specific tests to a new 'es.next' subdirectory
- Updated docs, targets, and test runners to reflect these changes

Resolves #3737.

JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu

tests/jerry/es.next/string-iterator.js

@@ -0,0 +1,77 @@
+// 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 {
+  String.prototype[Symbol.iterator].call(undefined);
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+try {
+  String.prototype[Symbol.iterator].call(Symbol('foo'));
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+var str = 'foobar';
+var iterator = str[Symbol.iterator]();
+
+try {
+  iterator.next.call(5);
+  assert (false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+try {
+  iterator.next.call({});
+  assert(false);
+} catch (e) {
+  assert(e instanceof TypeError);
+}
+
+var str = 'Example string.';
+var expected = ['E', 'x', 'a', 'm', 'p', 'l', 'e', ' ', 's', 't', 'r', 'i', 'n', 'g', '.'];
+
+var iterator = str[Symbol.iterator]();
+var next = iterator.next();
+var idx = 0;
+
+while (!next.done) {
+  assert(next.value === expected[idx++]);
+  assert(next.done === false);
+  next = iterator.next();
+}
+
+assert(next.value === undefined);
+
+var str = '^o𓙦һR񼴆]ŭ媖?᯾豼עW򏋁';
+var expected = ['^', 'o', '𓙦', 'һ', 'R', '񼴆', ']', 'ŭ', '媖', '?', '᯾', '豼', 'ע', 'W', '򏋁'];
+
+iterator = str[Symbol.iterator]();
+next = iterator.next();
+idx = 0;
+
+while (!next.done) {
+  assert(next.value === expected[idx++]);
+  assert(next.done === false);
+  next = iterator.next();
+}
+
+assert(next.value === undefined);
+
+assert(iterator.toString() === '[object String Iterator]');
+assert(iterator[Symbol.toStringTag] === 'String Iterator');