Rework ES2015 module system and add missing features. (#2792)

Co-authored-by: Dániel Bátyai <dbatyai@inf.u-szeged.hu>
JerryScript-DCO-1.0-Signed-off-by: Dániel Bátyai dbatyai@inf.u-szeged.hu
JerryScript-DCO-1.0-Signed-off-by: Daniel Vince vinced@inf.u-szeged.hu

tests/jerry/es2015/module-export-01.js

@@ -0,0 +1,41 @@
+/* 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.
+ */
+
+export {};
+export {a as aa,};
+export {b as bb, c as cc};
+export {d};
+export var x = 42;
+export function f(a) {return a;};
+export class Dog {
+  constructor (name) {
+    this.name = name;
+  }
+
+  speak() {
+    return this.name + " barks."
+  }
+};
+export default "default";
+
+var a = "a";
+var b = 5;
+var c = function(a) { return 2 * a;}
+var d = [1,2,3];
+
+assert (x === 42);
+assert (f(1) === 1);
+var dog = new Dog("Pluto")
+assert(dog.speak() === "Pluto barks.")