[JS BE] add runtime-function and intrinsics for es6-classes

libraries/stdlib/js-ir/runtime/constructFunction.kt

@@ -0,0 +1,13 @@
+/*
+ * Copyright 2010-2020 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.js
+
+/**
+ * @param CT is return type of calling constructor (uses in DCE)
+ */
+fun <CT> construct(constructorType: dynamic, resultType: dynamic, vararg args: Any?): Any {
+    return js("Reflect").construct(constructorType, args, resultType)
+}