move jscript transformer to the builtin-trailing group and perform transform on exit - closes #1652, fixes #1651

test/core/fixtures/transformation/jscript/arrow-function/exec.js

@@ -0,0 +1,9 @@
+class MyClass {
+  test() {
+    const that = this;
+    const func = () => this === that;
+    return func();
+  }
+}
+
+assert(new MyClass().test());