JS backend: added the support extension functions as expression.

js/js.translator/testData/expression/function/cases/expressionAsExtFunction.kt

@@ -0,0 +1,8 @@
+package foo
+
+fun box(): String {
+    val a = 23.{ Int.(a: Int) -> a * a + this }(3)
+    if (a != 32) return "a != 32, a = $a";
+
+    return "OK";
+}