JS backend: add the ability to get JS constructor function by class name and from instance. Support it for reified type parameters too. Add ability to get name of class.

#KT-5987 Fixed
 #KT-4115 Fixed

js/js.libraries/src/core/reflection.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * 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.
+ */
+
+package kotlin.js
+
+@native
+interface JsClass<T> {
+    val name: String
+}
+
+@native
+fun <T> jsClass(): JsClass<T> = noImpl
+
+val <T> T.jsClass: JsClass<T>
+    get() = js("Object").getPrototypeOf(this).constructor