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/multiDeclarationFor.kt

@@ -0,0 +1,17 @@
+data class A(val x: Int, val y: String)
+
+fun box(): String {
+    val arr = Array<A>(5) {
+        i -> A(i, i.toString())
+    }
+    
+    var sum = 0
+    var str = ""
+    
+    for ((x, y) in arr) {
+        sum += x
+        str += y
+    }
+    
+    return if (sum == 0+1+2+3+4 && str == "01234") "OK" else "Fail ${sum} ${str}"
+}