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/arrow-assignment.js

@@ -0,0 +1,46 @@
+/* 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 y = 0
+var prot = Object.getPrototypeOf(/ /)
+
+prot.setY = function (v) { y = v }
+
+assert(y === 0)
+// Since arrow function is an assignment expression, this affects certain constructs
+var f = x => {}
+/ /.setY(5)
+assert(y === 5)
+
+var s
+// This is not a function call
+assert(eval("s = x => { return 1 }\n(3)") === 3)
+assert(typeof s === "function")
+
+// This is a function call
+assert(eval("s = function () { return 1 }\n(3)") === 1)
+assert(s === 1)
+
+var f = 5 ? x => 1 : x => 2
+assert(f() === 1)
+
+var f = [x => 2][0]
+assert(f() === 2)
+
+var f = 123; f += x => y
+assert(typeof f === "string")
+
+// Comma operator
+assert(eval("x => {}, 5") === 5)