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/dataClasses/unitComponent.kt

@@ -0,0 +1,6 @@
+data class A(val x: Unit)
+
+fun box(): String {
+    val a = A(Unit)
+    return if (a.component1() is Unit) "OK" else "Fail ${a.component1()}"
+}