JS backend: fix KT-6112 jsonFromTuples is broken

#KT-6112 Fixed

js/js.libraries/src/core/json.kt

@@ -5,11 +5,13 @@ native public class Json() {
     public fun set(propertyName: String, value: Any?): Unit = noImpl
 }
 
-library("jsonFromTuples")
-public fun json(vararg pairs: Pair<String, Any?>): Json = noImpl
-
-library("jsonFromTuples")
-public fun json2(pairs: Array<Pair<String, Any?>>): Json = noImpl
+public fun json(vararg pairs: Pair<String, Any?>): Json {
+    var res: dynamic = js("({})")
+    for((name, value) in pairs) {
+        res[name] = value
+    }
+    return res
+}
 
 library("jsonAddProperties")
 public fun Json.add(other: Json): Json = noImpl

js/js.libraries/test/core/JsonTest.kt

@@ -0,0 +1,14 @@
+package test.js
+
+import kotlin.test.*
+import org.junit.Test as test
+
+class JsonTest {
+
+    test fun createJsonFromPairs() {
+        var obj = json(Pair("firstName", "John"), Pair("lastName", "Doe"), Pair("age", 30))
+        assertEquals("John", obj["firstName"], "firstName")
+        assertEquals("Doe", obj["lastName"], "lastName")
+        assertEquals(30, obj["age"], "age")
+    }
+}

js/js.tests/test/org/jetbrains/k2js/test/semantics/JsonTest.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2010-2014 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 org.jetbrains.k2js.test.semantics;
+
+import junit.framework.Test;
+
+@SuppressWarnings("JUnitTestCaseWithNoTests")
+public final class JsonTest extends JsUnitTestBase {
+    public static Test suite() throws Exception {
+        return createTestSuiteForFile("js/js.libraries/test/core/JsonTest.kt");
+    }
+}

js/js.translator/testData/kotlin_lib.js

@@ -955,16 +955,6 @@
         return new Kotlin.ArrayIterator(array);
     };
 
-    Kotlin.jsonFromTuples = function (pairArr) {
-        var i = pairArr.length;
-        var res = {};
-        while (i > 0) {
-            --i;
-            res[pairArr[i][0]] = pairArr[i][1];
-        }
-        return res;
-    };
-
     Kotlin.jsonAddProperties = function (obj1, obj2) {
         for (var p in obj2) {
             if (obj2.hasOwnProperty(p)) {