JS: move RTTI tests to proper location

js/js.translator/testData/box/rtti/sideEffectMethod.kt

@@ -0,0 +1,21 @@
+package foo
+
+var counter = 0
+
+class A {
+    fun getCounter(): Any? =
+        when (counter++) {
+            0 -> "0"
+            1 -> null
+            else -> counter
+        }
+}
+
+fun box(): String {
+    assertEquals(false, A().getCounter() is Int?, "(1)")
+    assertEquals(true, A().getCounter() is Int?, "(2)")
+    assertEquals(true, A().getCounter() is Int?, "(3)")
+    assertEquals(3, counter)
+
+    return "OK"
+}