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/functions/recursiveIncrementCall.kt

@@ -0,0 +1,12 @@
+operator fun String.inc() : String {
+    if (this == "") {
+        return "done"
+    }
+    var s = ""
+    return ++s
+}
+
+fun box() : String {
+    var s = "11test"
+    return if (++s == "done") "OK" else "FAIL"
+}