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/privateValParams.kt

@@ -0,0 +1,13 @@
+data class D(private val x: Long, private val y: Char) {
+    fun foo() = "${component1()}${component2()}"
+}
+
+fun box(): String {
+    val d1 = D(42L, 'a')
+    val d2 = D(42L, 'a')
+    if (d1 != d2) return "Fail equals"
+    if (d1.hashCode() != d2.hashCode()) return "Fail hashCode"
+    if (d1.toString() != d2.toString()) return "Fail toString"
+    if (d1.foo() != d2.foo()) return "Fail foo"
+    return "OK"
+}