backend/tests: Add blackbox tests from Kotlin JVM

Added tests from testData/codegen/box directory. There are blackbox tests
in other directories and they are to be added.

backend.native/tests/external/codegen/blackbox/controlStructures/forInSmartCastToArray.kt

@@ -0,0 +1,14 @@
+fun f(x: Any?): Any? {
+    if (x is Array<*>) {
+        for (i in x) {
+            return i
+        }
+    }
+    return "FAIL"
+}
+
+fun box(): String {
+    val a = arrayOfNulls<String>(1) as Array<String>
+    a[0] = "OK"
+    return f(a) as String
+}