JS: move expressions test to box tests

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

@@ -0,0 +1,14 @@
+package foo
+
+class Point(val x: Int, val y: Int) {
+    fun mul(): (scalar: Int) -> Point {
+        return { scalar: Int -> Point(x * scalar, y * scalar) }
+    }
+}
+
+val m = Point(2, 3).mul()
+
+fun box(): String {
+    val answer = m(5)
+    return if (answer.x == 10 && answer.y == 15) "OK" else "FAIL"
+}