JS backend: fix KT-6112 jsonFromTuples is broken

#KT-6112 Fixed

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")
+    }
+}