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/closures/localClassFunClosure.kt

@@ -0,0 +1,8 @@
+fun box(): String {
+    val o = "O"
+    fun ok() = o + "K"
+    class OK {
+        val ok = ok()
+    }
+    return OK().ok
+}