[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)
+}

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

@@ -99,6 +99,10 @@ internal fun newThrowable(message: String?, cause: Throwable?): Throwable {
 
 internal fun extendThrowable(this_: dynamic, message: String?, cause: Throwable?) {
     js("Error").call(this_)
+    setPropertiesToThrowableInstance(this_, message, cause)
+}
+
+internal fun setPropertiesToThrowableInstance(this_: dynamic, message: String?, cause: Throwable?) {
     if (!hasOwnPrototypeProperty(this_, "message")) {
         this_.message = message ?: cause?.toString() ?: undefined
     }