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/hashCode/genericNull.kt

@@ -0,0 +1,7 @@
+data class A<T>(val t: T)
+
+fun box(): String {
+    val h = A<String?>(null).hashCode()
+    if (h != 0) return "Fail $h"
+    return "OK"
+}