JS backend: added delegate property support.

js/js.translator/testFiles/delegateProperty/cases/topLevelVar.kt

@@ -0,0 +1,15 @@
+package foo
+class Delegate {
+    var inner = 1
+    fun get(t: Any?, p: PropertyMetadata): Int = inner
+    fun set(t: Any?, p: PropertyMetadata, i: Int) { inner = i }
+}
+
+var prop: Int by Delegate()
+
+fun box(): String {
+  if(prop != 1) return "fail get"
+  prop = 2
+  if (prop != 2) return "fail set"
+  return "OK"
+}