Spec compatibility for iteratorClose condition. (#6094)

* for-of: IteratorClose spec compatibility.

See #3:
https://tc39.github.io/ecma262/#sec-iteratorclose

* Update spec fixtures for for-of.

* Fix IteratorClose case for remap-async-to-generator.

* Fix IteratorClose case for async-generator-function test output.

* Modify few tests according to iteratorClose fix.

* Fix iteratorClose for helpers.slicedToArray also.

* Update iteratorClose fixture for commonjs.

packages/babel-plugin-transform-es2015-parameters/test/fixtures/parameters/rest-member-expression-deoptimisation/expected.js

@@ -164,7 +164,7 @@ function forOf() {
     _iteratorError = err;
   } finally {
     try {
-      if (!_iteratorNormalCompletion && _iterator.return) {
+      if (!_iteratorNormalCompletion && _iterator.return != null) {
         _iterator.return();
       }
     } finally {