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/classObjectWithPrivateGenericMember.kt

@@ -0,0 +1,15 @@
+class C() {
+    companion object {
+        private fun <T> create() = C()
+    }
+
+    class ZZZ {
+        val c = C.create<String>()
+    }
+}
+
+fun box(): String {
+    C.ZZZ().c
+    return "OK"
+}
+