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/defaultargs5.kt

@@ -0,0 +1,13 @@
+open abstract class B {
+    abstract fun foo2(arg: Int = 239) : Int
+}
+
+class C : B() {
+    override fun foo2(arg: Int) : Int = arg
+}
+
+fun box() : String {
+    if(C().foo2() != 239) return "fail"
+    if(C().foo2(10) != 10) return "fail"
+    return "OK"
+}