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/equals/sameinstance.kt

@@ -0,0 +1,7 @@
+data class A(val arg: Any? = null)
+
+fun box() : String {
+  val a = A()
+  val b = a
+  return if(b == a) "OK" else "fail"
+}