JS backend: add support multi declaration

js/js.translator/testFiles/multideclaration/cases/multiValForMap.kt

@@ -0,0 +1,40 @@
+package foo
+
+import java.util.HashMap
+
+
+public inline fun <K,V> Map<K,V>.iterator(): Iterator<Map.Entry<K,V>> {
+    val entrySet = this.entrySet()
+    return entrySet.iterator()
+}
+
+/** Returns the key of the entry */
+fun <K,V> Map.Entry<K,V>.component1() : K {
+    return getKey()
+}
+
+/** Returns the value of the entry */
+fun <K,V> Map.Entry<K,V>.component2() : V {
+    return getValue()
+}
+
+fun box(): String {
+    val map = HashMap<Int, String>()
+    map.put(1, "s1")
+    map.put(2, "s2")
+
+    var s1 = ""
+    var s2 = ""
+    for ((k,v) in map) {
+        when (k) {
+            2 -> s2 = v
+            1 -> s1 = v
+            else -> {}
+        }
+    }
+
+    if (s1 != "s1") return "s1 != 's1', it: ${s1}"
+    if (s2 != "s2") return "s2 != 's2', it: ${s2}"
+
+    return "OK"
+}