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/classes/overloadUnaryOperator.kt

@@ -0,0 +1,27 @@
+// WITH_RUNTIME
+class ArrayWrapper<T>() {
+    val contents = ArrayList<T>()
+
+    fun add(item: T) {
+       contents.add(item)
+    }
+
+    operator fun unaryMinus(): ArrayWrapper<T> {
+        val result = ArrayWrapper<T>()
+        result.contents.addAll(contents)
+        result.contents.reverse()
+        return result
+    }
+
+    operator fun get(index: Int): T {
+        return contents.get(index)!!
+    }
+}
+
+fun box(): String {
+    val v1 = ArrayWrapper<String>()
+    v1.add("foo")
+    v1.add("bar")
+    val v2 = -v1
+    return if (v2[0] == "bar" && v2[1] == "foo") "OK" else "fail"
+}