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/classes/delegationGenericArg.kt

@@ -0,0 +1,12 @@
+interface A<T> {
+    fun foo(t: T): String
+}
+
+class Derived(a: A<Int>) : A<Int> by a
+
+fun box(): String {
+    val o = object : A<Int> {
+        override fun foo(t: Int) = if (t == 42) "OK" else "Fail $t"
+    }
+    return Derived(o).foo(42)
+}