JS: move more test to box tests

js/js.translator/testData/box/examples/innerClass.kt

@@ -0,0 +1,19 @@
+class Outer(val foo: StringBuilder) {
+    inner class Inner() {
+        fun len(): Int {
+            return foo.length
+        }
+    }
+
+    fun test(): Inner {
+        return Inner()
+    }
+}
+
+fun box(): String {
+    val sb = StringBuilder("xyzzy")
+    val o = Outer(sb)
+    val i = o.test()
+    val l = i.len()
+    return if (l != 5) "fail" else "OK"
+}