JS: move expressions test to box tests

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

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